Methods of purifying Fc region containing proteins

ABSTRACT

The present application provides methods of purifying polypeptides having a Fc region, for example, antibodies or antibody fusions, by adsorbing the polypeptides to a Fc binding agent, such as, for example, Protein A or Protein G, followed by a wash with a divalent cation salt buffer to remove impurities and subsequent recovery of the adsorbed polypeptides. The present application also features methods of eluting the purified polypeptide as well as the incorporation of the methods within a purification train. Kits comprising components for carrying out the methods and instructions for use are also provided.

RELATED APPLICATIONS

This application claims priority to provisional patent application“METHODS OF PURIFYING Fc REGION CONTAINING PROTEINS”, filed Jun. 17,2005 having Ser. No. 60/691821. The entire content of this applicationis incorporated herein.

BACKGROUND OF THE INVENTION

Antibodies are powerful components of the immune system of many animalsand especially humans. Recent advances in recombinant technology haveallowed for the production of antibodies against virtually any target,for example, cancer cells, bacteria, and viruses. Typically, an antibodyis produced using a cell line that has been engineered to express theantibody at high levels. The engineered cell line is subsequently grownin a culture that comprises a complex mixture of sugars, amino acids,and growth factors, as well as various proteins, including for example,serum proteins. However, separation of complete antibodies from cellby-products and culture components to a purity sufficient for use inresearch or as therapeutics poses a formidable challenge. Thepurification of the antibody molecules is especially critical if theantibodies are to be used as a drug for administration to humans.

Traditional antibody purification schemes (or trains) often comprise achromatography step which exploits an ability of the antibody moleculeto preferentially bind or be retained by the solid phase (orfunctionalized solid phase) of a chromatography column compared to thebinding or retention of various impurities. Schemes have been proposedor carried out to purify antibodies which first bind CH2/CH3region-containing proteins to Protein A immobilized on a solid phase,followed by removal of impurities bound to the solid phase by washingthe solid phase with a hydrophobic electrolyte solvent and thesubsequent recovery of the CH2/CH3 region-containing proteins from thesolid phase. However, these schemes are limited in that the conditionsused to preferentially bind the CH2/CH3 region-containing proteins alsosupport binding of impurities (e.g., antibodies with incomplete CH2/CH3regions). In the development of human therapeutics, such impurities arehighly undesirable.

Accordingly, a need exists for improvements in the purification ofproteins or polypeptides having constant regions, in particular,proteins having Fc regions (e.g., antibodies), produced in cell culture.

SUMMARY OF THE INVENTION

In various aspects, the present invention features methods forseparating a protein having an Fc region from a source liquid comprisingthe protein and one or more impurities. In the methods of the invention,the protein having an Fc region (the target protein) is adsorbed to anFc binding agent and then the Fc binding agent is washed with a buffersolution containing a divalent cation salt to remove one or moreimpurities. The protein is then recovered from the Fc binding agent inan elution solution. The methods of the invention are particularlyuseful for removing impurities such as intron read through variantspecies (IRT), under disulfide bonded species (UDB) and/or low molecularweight variant species (LMW). The methods of the invention also areeffective in removing impurities such as host cell proteins (HCP) andDNA.

The methods of the present invention comprise one or morechromatographic separation steps and in addition can comprise one ormore filtration steps. The chromatographic separation steps can becontinuous or discontinuous (e.g., a batch approach), or a combinationof both. In various embodiments, the methods comprise one or morefiltration steps, for example, to remove viruses, concentrate and bufferthe solution containing the target protein, and to remove microbialcontaminants.

In various embodiments, the Fc region containing protein is anantigen-binding polypeptide (e.g., an antibody or fragment thereof) oran immunoadhesin (e.g., a TNF receptor immunoadhesin). In variousembodiments, the Fc region containing protein is an antibody fusion, amurine antibody, a chimeric antibody, or a humanized antibody. In apreferred embodiment, the Fc region containing protein is a human orhumanized anti-IL-13 antibody. Alternatively, in other embodiments, theFc region containing protein can bind an antigen such as Aβ, CD3, CD52,VEGF, EGFR, CD33, CD20, HER-2, TNFα, CD25, RSV, IgE, gp IIb/IIIa, CD11aor α4 integrin

In various embodiments, the Fc region containing protein isrecombinantly produced. In various embodiments, the Fc region containingprotein is recombinantly produced in a Chinese Hamster Ovary (CHO) cell.

In various embodiments, the one or more impurities comprise one or moreof a host cell protein, a host cell DNA, a cell culture protein, anundesired species of the protein having an Fc region, and mixturesthereof. For example, in various embodiments the undesired species ofthe protein having an Fc region comprises one or more of antibody chainsor fragments thereof having intron read through sequence, one or moreantibody chains or fragments thereof having an improper disulfidelinkage, a half-antibody or fragment thereof, a light chain dimer orfragment thereof, and a heavy chain dimer or fragment thereof.

In one aspect, the methods of the present invention purify a proteinhaving an Fc region from a source liquid comprising the protein and oneor more impurities by first adsorbing the protein to an Fc bindingagent, followed by washing the Fc binding agent with a buffer solutioncontaining a divalent cation salt to remove one or more impurities, andsubsequently recovering the protein from the Fc binding agent. Invarious embodiments, the steps of adsorbing the protein to an Fc bindingagent and washing the Fc binding agent with a buffer solution containinga divalent cation salt, are performed at temperature in the rangebetween about 2° C. to about 24° C. In various embodiments, the step ofrecovering the protein from the Fc binding agent comprises eluting theprotein using an elution buffer having a pH in the range from about 2.0to about 6.5.

In various embodiments, the Fc region binding agent comprises one ormore of Protein A and Protein G. In a preferred embodiment, the Fcbinding agent is immobilized on a solid phase. This solid phase cancomprise, for example, one or more of a bead, an agarose matrix, silica,and mixtures thereof.

The divalent cation salt present in the buffer that is used to wash theFc binding agent can comprise, for example, a chaotropic salt. Suitabledivalent cation salts for preparation of the wash buffer solutioninclude, but are not limited to, magnesium chloride, calcium chloride,nickel chloride and mixtures thereof. In various embodiments, suitabledivalent cation salts for preparation of the wash buffer solutioninclude, but are not limited to, thiocyanate (SCN⁻), perchlorate (ClO₄⁻), nitrate (NO₃ ⁻), chloride, and bromide salts of divalent group II(e.g., magnesium, calcium, barium, etc.) cations, divalent transitionmetal (e.g., copper, nickel, manganese, etc.) cations, and combinationsof these salts.

In various embodiments, the buffer solution containing the divalentcation salt has a pH value in the range between about 4 to about 9, andin some embodiments, between about 4 to about 8, between about 4.5 toabout 7.5 or between about 6 to about 8. Values and ranges includedand/or intermediate within the ranges set forth herein are also intendedto be within the scope of the present invention. For example, thedivalent cation salt has a pH value between about 7.1 to about 7.9,between about 7.2 to about 7.9, between about 7.3 to about 7.7, betweenabout 7.4 to about 7.6, between about 4 to about 5, between about 5 toabout 6, between about 6 to about 7, or between about 8 to about 9.

Moreover, ranges having values recited herein as an upper or lower limitare intended to be within the scope of the present invention. Forexample, the divalent cation salt has a pH of at least about (or about)4.5, 5, 5.5, 6, 6.5, 7, 7.5, or 8.

In various embodiments, the buffer solution has a divalent cation saltconcentration in the range between about 0.1 M to about 5 M, and in someembodiments between about 0.5 M to about 3M, between about 1.0 M toabout 3 M or between about 0.6 M to about 2.5 M. For example, thedivalent cation buffer may comprise at least about 0.6 M CaCl₂ or atleast about 2M MgCl₂ or at least about 2M CaCl₂. Values and rangesincluded and/or intermediate within the ranges set forth herein are alsointended to be within the scope of the present invention. For example,the buffer solution has a divalent cation salt concentration betweenabout 0.5 M to about 0.75 M, between about 0.5 M to about 0.8 M, betweenabout 0.5 M to about 0.9 M, between about 0.5 M to 1.0 M, between about0.5 M to 2 M, between about 1.5 M to about 2.0 M, between about 1.5 M toabout 2.5 M, between about 1.5 M to about 3.0 M, or between about 2.5 Mto about 3 M.

Moreover, ranges having values recited herein as an upper or lower limitare intended to be within the scope of the present invention. Forexample, the buffer solution has a divalent cation salt concentration ofat least about (or about) 0.6 M, 1 M, 1.5 M, 2 M, 2.5 M, or 3 M. Invarious embodiments, the buffer solution containing a divalent cationsalt has a temperature in the range between about 2° C. to about 24° C.

In various embodiments, the step of recovering the protein from the Fcbinding agent comprises eluting the protein using an elution bufferhaving a pH in the range of about 2.0 to about 6.5, preferably in therange of about 2.0 to about 4.0, more preferably in the range of about2.5 to about 3.5. Values and ranges included and/or intermediate withinthe ranges set forth herein are also intended to be within the scope ofthe present invention. For example, the elution buffer has a pH ofbetween about 2 to about 3 or between about 3 to about 4.

Moreover, ranges having values recited herein as an upper or lower limitare intended to be within the scope of the present invention. Forexample, the elution buffer has a pH of at least about (or about) 2,2.5, 3, 3.5 or 4.

In various embodiments, the recovered proteins can be subjected toadditional purification steps either prior to, or after, the Fc bindingagent chromatography step. For example, exemplary further purificationsteps include, but are not limited to: anion exchange chromatography,cation exchange chromatography, immobilized metal affinitychromatography, hydrophobic interaction chromatography (HIC),hydroxyapatite chromatography, dialysis, affinity chromatography,ammonium sulphate precipitation, ethanol precipitation, reverse phaseHPLC (RP-HPLC), chromatofocusing, ultrafiltration, diafiltration,microfiltration, and gel filtration. In various embodiments, the Fcbinding agent chromatography step is followed by an anion exchangechromatography and a HIC step. In various embodiments, thechromatography steps are further followed by a virus filtration step, anultrafiltration/diafiltration step, and/or a microbial contaminantfiltration step.

In one aspect, the present invention provides methods for purifying anantibody from an impurity-containing solution thereof. In variousembodiments, the methods comprise first adsorbing the protein to an Fcbinding agent, followed by washing the Fc binding agent with a buffersolution containing a divalent cation salt to remove one or moreimpurities, and subsequently recovering the protein from the Fc bindingagent to produce a first eluent pool.

In various embodiments, the purification process continues withsubjecting the first eluent pool to ion exchange chromatography bycontacting an ion exchange resin with the first eluent pool such thatthe target protein does not adsorb to the resin and recovering theflow-through target protein to produce a second eluent pool. In variousembodiments, the ion exchange chromatography step further compriseswashing the ion exchange resin with a buffered wash solution to recoverat least a portion of any adsorbed target protein.

In various embodiments, the purification process continues withsubjecting the second eluent pool to hydrophobic interactionchromatography by adsorbing the target protein to a hydrophobicinteraction resin (e.g., a solid phase functionalized with hydrophobicligands), washing the hydrophobic interaction resin with a buffered washsolution with an ionic strength which does not substantially elute thetarget protein, and recovering the purified target protein (typicallyusing an elution buffer with an ionic strength low enough to desorb thetarget protein from the hydrophobic interaction resin).

In preferred embodiments of the various aspects of the inventions, theFc binding agent is immobilized on a solid phase, which is preferablyequilibrated with a suitable buffer prior to contact with the sourceliquid. The solid phase is preferably a column comprising agaroseimmobilizing the Fc binding agent. In various embodiments, the column iscoated with a reagent, such as glycerol, to decrease or preventnonspecific adherence to the column.

In various embodiments, the proteins purified by methods of the presentinvention can be formulated in a pharmaceutically acceptable carrier andused for various diagnostic, therapeutic or other uses known for suchmolecules.

In various aspects, the present invention provides methods for purifyingan Fc region containing protein from a solution containing the proteinand intron read-through variants (IRT) thereof. In featured aspects,methods of the present invention are used to reduce the levels of one ormore intron read-through variant species in a protein preparation, forexample, in an antibody preparation. In various embodiments, the proteinrecovered from the Fc binding agent has a level of intron read-throughvariants that is at least 5 fold less than the level of intronread-through variants in the source liquid, and in some embodiments atleast 10 fold less than the level of intron read-through variants in thesource liquid. In various embodiments, the intron read-through variantscomprise less than about 1.0%, 0.8%, 0.5%, 0.2% or 0.1% of the speciesof said protein in the solution containing said protein recovered fromthe Fc binding agent.

In various aspects, the present invention provides methods for purifyingan Fc region containing protein from a solution containing the proteinand low molecular weight variants (LMW) thereof. In featured aspects,methods of the present invention are used to reduce the levels of one ormore low molecular weight variant species in a protein preparation, forexample, in an antibody preparation. In various embodiments, the proteinrecovered from the Fc binding agent has a level of low molecular weightvariants that is at least 5 fold less than the level of low molecularweight variants in the source liquid, and in some embodiments at least10 fold less than the level of low molecular weight variants in thesource liquid. In various embodiments, the low molecular weight variantscomprise less than about 1.0%, 0.8%, 0.5%, 0.2% or 0.1% of the speciesof said protein in the solution containing said protein recovered fromthe Fc binding agent.

In various aspects, the present invention provides methods for purifyingan Fc region containing protein from a solution containing the proteinand under disulfide bonded variants (UDB) thereof. In featured aspects,methods of the present invention are used to reduce the levels of one ormore under disulfide bonded variant species in a protein preparation,for example, in an antibody preparation. In various embodiments, theprotein recovered from the Fc binding agent has a level of underdisulfide bonded variants that is at least 5 fold less than the level ofunder disulfide bonded variants in the source liquid, and in someembodiments at least 10 fold less than the level of under disulfidebonded variants in the source liquid. In various embodiments, the underdisulfide bonded variants comprise less than about 20%, 15%, 10%, 5%,2%, or 1% of the species of said protein in the solution containing saidprotein recovered from the Fc binding agent.

In another aspect, the invention pertains to an Fc region containingprotein purified according to the method of invention.

In another aspect, the present invention provides a system suitable forperforming any of the methods that comprise at least the steps of firstadsorbing the protein to an Fc binding agent, followed by washing the Fcbinding agent with a buffer solution containing a divalent cation saltto remove one or more impurities, and subsequently recovering theprotein from the Fc binding agent.

In another aspects, the present invention provides a purification trainfor performing any of the methods that comprise at least the steps offirst adsorbing the protein to an Fc binding agent, followed by washingthe Fc binding agent with a buffer solution containing a divalent cationsalt to remove one or more impurities, and subsequently recovering theprotein from the Fc binding agent.

The present invention also features, in various aspects, kits for use inperforming one or more of the methods of the present invention. Invarious embodiments, the kit comprises at least one reagent andinstructions for use of the kit. For example, a kit can comprise one ormore reagents such as an Fc binding agent, a divalent cation salt andreagents for the preparation of buffer wash solution containing adivalent cation salt, along with instructions for use of the kit.

DETAILED DESCRIPTION OF THE INVENTION

Prior to further describing the invention, it may be helpful to anunderstanding thereof to set forth definitions of certain terms to beused herein. The definitions set forth herein have been grouped for easeof reference only and not by way of limitation.

Protein Related Definitions

In various aspects, the present invention provides methods for purifyingan Fc region containing protein from a solution containing the proteinand one or more read-through variants thereof, such as, for example,intron read-through variants. In featured aspects, methods of thepresent invention are used to reduce the levels of one or more intronread-through (IRT) variant species in a protein preparation, forexample, in an antibody preparation. The terms “intron read-throughvariant,” and “intron read-through variant species” are usedinterchangeably herein and refer to the product of a process where inthe synthesis of the Fc region containing protein of interest (e.g., thetarget protein) polypeptide chain elongation is terminated prior totranscription of a coding region by a stop codon in the intron prior tothe coding region. The result is a variant of the protein of interest(i.e., an intron read-through variant) with one or more incomplete ormissing domains. Such introns can contain more than one stop codonresulting in the possibility of producing several different intronread-through variants.

The term “under disulfide bonded variant” or “UDB” refers to any specieswhere at least one disulfide bond is missing. The missing disulfide bondcan be either an interchain disulfide bond or an intrachain disulfidebond or a combination of the two.

The term “low molecular weight species” or “LMW” species refers tovariants of the Fc region containing protein including a protein speciesthat consists of free heavy chain, free light chain, IRT species,half-molecule, and three-quarters-molecule, or mixtures thereof.

Protein A is an about 42 kD cell wall protein found in most strains ofStaphylococcus aureas which binds with high affinity (about 10⁻⁸ M tohuman IgG) to the Fc region of antibodies. As used herein, the term“Protein A” encompasses Protein A recovered from a native sourcethereof, Protein A produced synthetically (e.g. by peptide synthesis, byrecombinant techniques, etc.), and variants thereof which retain theability to bind proteins which have a CH2/CH3 region.

Protein G is a cell wall protein from group G streptococci. Protein G isa type III Fc-receptor which binds with high affinity to the Fc regionof antibodies, in particular, IgG antibodies. As used herein, the term“Protein G” encompasses Protein G recovered from a native sourcethereof, Protein G produced synthetically (e.g., by peptide synthesis,by recombinant techniques, etc.), and variants thereof, which retain theability to bind proteins which have an Fc region.

The term “antibody” or “immunoglobulin” (used interchangeably herein)refers to an antigen-binding protein having a basic four-polypeptidechain structure consisting of two heavy and two light chains, saidchains being stabilized, for example, by interchain disulfide bonds,which has the ability to specifically bind antigen. Both heavy and lightchains are folded into domains.

The term “domain” refers to a globular region of a heavy or light chainpolypeptide comprising peptide loops (e.g., comprising 3 to 4 peptideloops) stabilized, for example, by β-pleated sheet and/or intrachaindisulfide bond. Domains are further referred to herein as “constant” or“variable”, based on the relative lack of sequence variation within thedomains of various class members in the case of a “constant” domain, orthe significant variation within the domains of various class members inthe case of a “variable” domain. “Constant” domains on the light chainare referred to interchangeably as “light chain constant regions”,“light chain constant domains”, “CL” regions or “CL” domains).“Constant” domains on the heavy chain are referred to interchangeably as“heavy chain constant regions”, “heavy chain constant domains”, “CH”regions or “CH” domains). “Variable” domains on the light chain arereferred to interchangeably as “light chain variable regions”, “lightchain variable domains”, “VL” regions or “VL” domains). “Variable”domains on the heavy chain are referred to interchangeably as “heavychain variable regions”, “heavy chain variable domains”, “VH” regions or“VH” domains).

The term “fragment” refers to a part or portion of an antibody orantibody chain comprising fewer amino acid residues than an intact orcomplete antibody or antibody chain. Fragments can be obtained viachemical or enzymatic treatment of an intact or complete antibody orantibody chain. Fragments can also be obtained by recombinant means.Exemplary fragments include Fab, Fab′, F(ab′)2, Fabc and/or Fvfragments. The term “antigen-binding fragment” refers to a polypeptidefragment of an immunoglobulin or antibody that binds antigen or competeswith the intact antibody from which they were derived for specificantigen binding.

The terms “antibody fusion protein” and “antibody fusion” refers to afusion protein including all or a portion of an antibody fused to atleast one non-antibody protein portion or polypeptide. Fusion isgenerally accomplished by genetic engineering of the gene encoding saidprotein. Additional exemplary antibody fusion proteins include the cellreceptor binding portion of an antibody (including the Fc region) fusedto all or a portion of another soluble or cellular biological protein,for example a receptor (cellular or soluble) or portion thereof, acytokine or portion thereof, an enzyme or portion thereof, etc. Suchantibody fusion proteins that comprise the Fc region of the antibodyfused to another protein are also referred to in the art as Fc fusionproteins.

The term “Fc binding agent” refers to a molecule that is capable ofbinding to the Fc region of an antibody (e.g., an IgG antibody)including, but not limited to, a complement protein, an Fc receptor or abacterial-derived protein, such as Protein A or Protein G, that has highaffinity for the Fc region of an antibody.

The term “Fc region” refers to a C-terminal region of an IgG antibody,in particular, the C-terminal region of the heavy chain(s) of said IgGantibody. Although the boundaries of the Fc region of an IgG heavy chaincan vary slightly, a Fc region is typically defined as spanning fromabout amino acid residue Cys226 to the carboxyl-terminus of an IgG heavychain(s).

Chromatography Related Definitions

The term “source liquid”, as used herein, refers to a liquid containingat least one target substance which is sought to be purified from othersubstances also present. Source liquids can, for example, be aqueoussolutions, organic solvent systems, or aqueous/organic solvent mixturesor solutions. The source liquids are often complex mixtures or solutionscontaining many biological molecules (such as proteins, antibodies,hormones, and viruses), small molecules (such as salts, sugars, lipids,etc.) and even particulate matter. While a typical source liquid ofbiological origin may begin as an aqueous solution or suspension, it mayalso contain organic solvents used in earlier separation steps such assolvent precipitations, extractions, and the like. Examples of sourceliquids that may contain valuable biological substances amenable to thepurification by various embodiments the present invention include, butare not limited to, a culture supernatant from a bioreactor, ahomogenized cell suspension, plasma, plasma fractions, and milk.

The term “target substance” or “target protein” refers herein to the oneor more desired Fc region containing proteins to be purified from thesource liquid. The target substance may be present in the source liquidas a suspension or in solution.

The term “impurities” refers to materials in the source liquid that aredifferent from the target substance(s) and are desirably excluded fromthe final target substance product(s). Typical impurities includenucleic acids, proteins (including intron-read-through species, lowmolecular weight species and under disulfide bonded species), peptides,endotoxins, viruses and small molecules.

As used herein, the term “solid phase” refers to a non-aqueous matrixwith which a target substance interacts during purification or to whichan Fc binding agent can adhere. Suitable solid phase materials include,but are not limited to, glass, silica (e.g. silica gel), polysaccharides(e.g., a polysaccharide matrix) such as agarose and cellulose, organicpolymers such as polyacrylamide, methylmethacrylate, andpolystyrene-divinylbenzene copolymers such as for example Amberlite™resin, (commercially available from Rohm & Haas Chemical Co.,Philadelphia, Pa.). The solid phase can be selected from any of thegroups of resins commonly described as affinity, ion exchange and ioncapture resins. The solid phase can be, for example, a purificationcolumn, a discontinuous phase of discrete particles, or a combinationthereof. The solid phase can be of porous or nonporous character, andcan be compressible or incompressible. In various embodiments, the solidphase is a polymeric matrix or an agarose particle or bead. In variousembodiments, the solid phase can be coated with a reagent (such asglycerol), for example, to prevent nonspecific adherence of impuritiesto the solid phase. An Fc binding solid phase need only possess achemistry or an associated ligand that will permit Fc binding agent toadhere to the surface of the solid phase. Preferred solid phasematerials will be physically and chemically resilient to the conditionsemployed in the purification process including pumping and cross-flowfiltration, and temperatures, pH, and other aspects of the liquidsemployed.

“Affinity ligand” refers to a moiety that binds selectively orpreferentially to a component of the source liquid through a specificinteraction with a binding site of the component. In the presentinvention, the affinity ligand (e.g., an Fc binding agent) is typicallyimmobilized to a solid phase such as a resin. Examples of affinityligands that can be bound to the resin support to provide chromatographyresins useful in the process of the present invention include, but arenot limited to, Protein A, Protein G, and their analogs, whichselectively bind to a protein Fc region. Methods of binding affinityligands to solid support materials are well known in the purificationart. See, e.g., the reference texts Affinity Separations: A PracticalApproach (Practical Approach Series), Paul Matejtschuk (Editor), Irl Pr:1997; and Affinity Chromatography, Herbert Schott, Marcel Dekker, NewYork: 1997.

“Affinity chromatography resin” or “affinity resin” refers to achromatography resin that comprises a solid phase or substrate withaffinity ligands bound to its surfaces.

“Ion exchange chromatography resin” or “ion exchange resin” refers to asolid support to which are covalently bound ligands that bear a positiveor negative charge, and which thus has free counterions available forexchange with ions in a solution with which the ion exchange resin iscontacted.

“Cation exchange resins” refers to an ion exchange resin with covalentlybound negatively charged ligands, and which thus has free cations forexchange with cations in a solution with which the resin is contacted. Awide variety of cation exchange resins are known in the art, forexample, those wherein the covalently bound groups are carboxylate orsulfonate. Commercially available cation exchange resins includeCMC-cellulose, SP-Sephadex™, and Fast S-Sepharose™ (the latter two beingcommercially available from Pharmacia).

“Anion exchange resins” refers to an ion exchange resin with covalentlybound positively charged groups, such as quaternary amino groups.Commercially available anion exchange resins include DEAE cellulose,TMAE, QAE Sephadex™, and Fast Q Sepharose™ (the latter two beingcommercially available from Pharmacia).

As used herein, the term “chaotropic salt” refers to a salt whichcomprises one or more ionic components that are low in the lyotropicseries that are able to penetrate protein hydration shells and binddirectly to their surfaces. This disrupts cohydrative association,favoring protein solubilization. Examples of chaotropic salts include,but are not limited to, halide salts of the Group II elements (e.g.,calcium chloride, magnesium chloride, barium chloride, calcium bromide,magnesium bromide, barium bromide, calcium iodide, magnesium iodide,barium iodide).

Examples of suitable divalent cations salts include, but are not limitedto, salts of Mn²⁺, Ni²⁺ or Cu²⁺, Mg²⁺, Ca²⁺ and Ba²⁺ with thiocyanate(SCN⁻), perchlorate (ClO₄ ⁻), nitrate (NO₃ ⁻), chloride (Cl⁻), andbromide (Br⁻); and combinations thereof.

In certain embodiments, the divalent cation salt comprises a divalentcation (e.g., Mg²⁺, Ca²⁺, Ni²⁺ or Ba²⁺). Preferred chaotropic salts foruse in the featured processes are MgCl₂, NiCl₂ and CaCl₂. After thedivalent cation salt wash step, the target protein is eluted from theaffinity chromatography matrix.

A “buffer” is a substance which, by its presence in solution, increasesthe amount of acid or alkali that must be added to cause unit change inpH. A buffered solution resists changes in pH by the action of itsacid-base conjugate components. Buffered solutions for use withbiological reagents are generally capable of maintaining a constantconcentration of hydrogen ions such that the pH of the solution iswithin a physiological range. The term “physiological pH” refers to thepH of mammalian blood (i.e., 7.38 or about 7.4). Thus a physiologic pHrange is from about 7.2 to 7.6. Traditional buffer components include,but are not limited to, organic and inorganic salts, acids and bases.Exemplary buffers for use in purification of biological molecules (e.g.,protein molecules) include the zwitterionic or “Good” Buffers, see e.g.,Good et al. (1966) Biochemistry 5:467 and Good and Izawa (1972) MethodsEnzymol. 24:62. Exemplary buffers include but are not limited to TES,MES, PIPES, HEPES, MOPS, MOPSO, TRICINE and BICINE.

The “equilibration buffer” herein is a buffer used to prepare the Fcbinding reagent, solid phase, or both, for loading of the source liquidcontaining the target protein. The equilibration buffer is preferablyisotonic and commonly has a pH in the range from about 6 to about 8. The“loading buffer” is a buffer used to load the source liquid containingthe Fc region containing protein and impurities onto the solid phase towhich the Fc binding agent is immobilized. Often, the equilibration andloading buffers are the same. The “elution buffer” is used to elute theFc region-containing protein from the immobilized Fc binding agent.Preferably the elution buffer has a low pH and thereby disruptsinteractions between the Fc binding agent and the protein of interest.Preferably, the low pH elution buffer has a pH in the range from about 2to about 5, most preferably in the range from about 3 to about 4.Examples of buffers that will control the pH within this range includeglycine, phosphate, acetate, citrate and ammonium buffers, as well ascombinations of these. The preferred such buffers are citrate andacetate buffers, most preferably sodium citrate or sodium acetatebuffers. Other elution buffers are contemplated including high pHbuffers (e.g. those having a pH of 9 or more) or buffers comprising acompound or composition such as MgCl₂ (2 mM) for eluting the protein ofinterest.

“Wash liquid” or “wash buffer” as used herein all refer herein to theliquid used to carry away impurities from the chromatography resin towhich is bound the target substance. More than one wash liquid can beemployed sequentially, e.g., with the successive wash liquids havingvarying properties such as pH, conductivity, solvent concentration,etc., designed to dissociate and remove varying types of impurities thatare non-specifically associated with the chromatography resin.

“Elution liquid” or “elution buffer” refers herein to the liquid that isused to dissociate the target substance from the chromatography resinafter it has been washed with one or more wash liquids. The elutionliquid acts to dissociate the target substance without denaturing itirreversibly. Typical elution liquids are well known in thechromatography art and may have higher concentrations of salts, freeaffinity ligands or analogs, or other substances that promotedissociation of the target substance from the chromatography resin.“Elution conditions” refers to process conditions imposed on the targetsubstance-bound chromatography resin that dissociate the targetsubstance from the chromatography resin, such as the contacting of thetarget substance-bound chromatography resin with an elution liquid orelution buffer to produce such dissociation.

“Cleaning liquid” or “cleaning buffer” refers herein to the liquid thatis used to wash the chromatography resin after the completion of thepurification process. The cleaning liquid may contain a detergent, avirus-inactivating agent, or relatively high concentrations of salts,and may have a higher or lower pH than the liquids used during thepurification process. Its purpose is to decontaminate the chromatographyresin to render it ready for reuse. Typical cleaning liquids arewell-known in the chromatography art.

“Storage liquid” or “storage buffer” refers herein to the liquid inwhich the chromatography resin is suspended between uses. Storageliquids, in addition to buffering ions, may also contain microbicides orother preservatives. Such storage liquids are well known in thechromatography art.

In various aspects, the present invention features methods for purifyinga protein having an Fc region from a source liquid comprising theprotein and one or more impurities by adsorbing the protein to an Fcbinding agent, followed by washing the Fc binding agent with a buffersolution containing a divalent cation salt to remove one or moreimpurities, and subsequently recovering the protein from the Fc bindingagent. Suitable Fc binding agents include, but are not limited to,Protein A and Protein G.

The present invention features processes for the purification of Fcregion containing proteins, for example, antibodies. Exemplarypurification processes include an affinity chromatography step. Theaffinity chromatography step can be continuous, discontinuous, or acombination of both. For example, the affinity chromatography step canbe performed as a discontinuous process, such as, for example, a batchprocess. Affinity chromatography is the process of bioselectiveadsorption and subsequent recovery of a target compound from animmobilized ligand. This process allows for the highly specific andefficient purification of the target compound. The process requires theutilization of an appropriately selective ligand (e.g., Fc bindingagent) which will bind the target compound (e.g., Fc region containingprotein) generally with a dissociation constant in the range of 10⁻⁴ to10⁻⁸, while permitting recovery under mild conditions. The ligand isgenerally immobilized on a beaded and porous matrix which may be in theform of a column packing or batchwise adsorption medium.

A preferred binding agent is Protein A. Protein A binds the Fc region ofimmunoglobulins. Protein A consists of six regions, five of which bindIgG. It binds with high affinity to human IgG₁, IgG₂ and IgG₄, as wellas mouse IgG_(2a), IgG_(2b) and IgG₃. Protein A binds with moderateaffinity to human IgD, IgM, IgA and IgE as well as mouse IgG₁. As anaffinity ligand, Protein A is immobilized to a matrix so that theseregions are free to bind. One molecule of immobilized Protein A can bindat least two molecules of IgG. Native and recombinant versions ofProtein A share similar specificity for the Fc region of IgG.Recombinant Protein A (rprotein A) can be engineered to include, forexample, a C-terminal cysteine, and can be immobilized via thioetsercoupling to a solid phase matrix. Such coupling results in enhancedbinding capacity of the protein A.

An alternative binding agent is Protein G. Protein G is specific forIgG, binding with high affinity for human IgG₁, IgG₂, IgG₃ and IgG₄, aswell as mouse IgG₁ and IgG₃. Protein G PLUS has moderate affinity forhuman IgG₄ and mouse IgG_(2a), IgG_(2b) and IgG₃. Recombinant protein G(rProteinG) can be engineered to delete the albumin-binding region ofthe native protein. Recombinant Protein G contains two Fc bindingregions.

An alternative binding agent is Protein A/G. Protein A/G is agenetically-engineered protein that combines the IgG binding profiles ofboth Protein A and Protein G. It is a gene fusion product secreted froma nonpathogenic form of Bacillus. Protein A/G contains four Fc bindingdomains from Protein A and two from Protein G. Protein A/G is not as pHdependent as Protein A, but otherwise has the additive properties ofProtein A and G.

Protein A/G binds to all human IgG subclasses, particularly suitable forpurification of polyclonal or monoclonal IgG antibodies whose subclasseshave not been determined. In addition, it binds to IgA, IgE, IgM and (toa lesser extent) IgD. Protein A/G also binds well to all mouse IgGsubclasses, particularly suitable for purification of mouse monoclonalantibodies from IgG subclasses, without interference from IgA, IgM andmurine serum albumin. (See e.g., Sikkema. (1989) Amer. Biotech. Lab 7,42.) Individual subclasses of mouse monoclonals can have a strongeraffinity for the chimeric Protein A/G than to either Protein A orProtein G. (See e.g., Eliasson et al. (1988) J. Biol. Chem. 263,4323-4327.)

In the present invention, the immobilized Fc binding agent (e.g.,Protein A) is washed with a divalent cation salt solution to removeimpurities. In particular, it has been discovered that undesirableimpurities produced as a result of recombinant antibody expressiontechnologies can be removed using a divalent cation salt wash step.

The methods of the present invention can optionally include purificationsteps subsequent to the affinity chromatography and divalent cation washstep. Subsequent purification steps can include an ion exchangechromatography step and/or a hydrophobic interaction chromatography(HIC) step. Subsequent chromatography steps can be continuous,discontinuous (e.g., such as a batch process), or a combination of both.Ion exchange chromatography separates molecules based on differencesbetween the overall charge of the proteins. The target protein must havea charge opposite that of the functional group attached to the resin inorder to bind. For example, antibodies, which generally have an overallpositive charge, will bind well to cation exchangers, which containnegatively charged functional groups. Because this interaction is ionic,binding must take place under low ionic conditions. Elution is achievedby increasing the ionic strength to break up the ionic interaction, orby changing the pH of the protein.

Whereas ion exchange chromatography relies on the charges of proteins toisolate them, hydrophobic interaction chromatography uses thehydrophobic properties of some proteins. Hydrophobic groups on theprotein bind to hydrophilic groups on the column. The more hydrophobic aprotein is, the stronger it will bind to the column. The HIC stepremoves, for example, host cell derived impurities (e.g., DNA and otherhigh and low molecular weight product-related species). Furtherpurification steps can include virus removing steps as well asultrafiltration and/or diafiltration steps, as described herein.

In various embodiments, the Fc region containing protein is an antibodyor an antibody fusion protein having an Fc region that binds to an Fcreceptor of the Fc binding agent. The use of the buffer solutioncontaining a divalent cation salt to wash the Fc binding agent allowsfor greater removal of impurities, such as, for example, read-throughvariants and constant region containing fragments (including LMW and UDBspecies), of the protein of interest (e.g., the target substance in thesource liquid).

The methods of the present invention comprise one or morechromatographic separation steps and in addition can comprise one ormore filtration steps for separating a protein having an Fc region (“thetarget protein”) from impurities in a source liquid. For example, thesource liquid may be filtered, centrifuged or otherwise processed toremove particulate debris and the like before contacting the sourceliquid with the Fc binding agent. For example, using recombinanttechniques, proteins can be produced intracellularly, in the periplasmicspace, or secreted directly into the culture medium. If the protein isproduced intracellularly, the particulate debris, either host cells orlysed fragments, can be removed, for example, by centrifugation orultrafiltration. Where the protein is secreted into the medium, therecombinant host cells can be separated from the cell culture medium,for example, by tangential flow filtration.

In various embodiments, the source liquid containing the target proteinis contacted with an Fc binding agent (preferably immobilized on a solidphase and equilibrated with a suitable buffer) such that the targetprotein adsorbs to the Fc binding agent (e.g., an immobilized Fc bindingagent). The source liquid is contacted with the Fc binding agent (e.g.,an immobilized Fc binding agent) in a loading buffer which may be thesame as the equilibration buffer. As the impurity-containing sourceliquid flows through the solid phase, the target protein is adsorbed tothe Fc binding agent and various other impurities (such as host cellproteins, where the target protein is produced in a recombinant hostcell, or other process-derived impurities) flow-through or bindnonspecifically to the solid phase. In various embodiments, the Fcbinding agent is Protein A, and the equilibration buffer can be 20 mMTris, 0.15 M NaCl, pH 7.5. Other suitable equilibration buffers include,for example, BIS, HEPES, etc., at physiological concentrations, forexample, concentration in the range between about 0.5 mM and about 100mM (e.g., 10 mM, 20 mM, 50 mM, etc.), and physiological saltconcentrations (e.g., about 0.15 mM NaCl), and at pH from 5.0-9.0.

The solid phase is preferably an agarose (e.g., Sepharose) bead orparticle for immobilizing the Fc binding agent. In various embodiments,the column is coated with a reagent, such as glycerol, to decrease orprevent nonspecific adherence to the column. In various embodiments, theFc binding agent is Protein A. The rmp Protein A Sepharose™ Fast Flow(FF) column, commercially available from Amersham Biosciences, is anexample of a suitable Protein A column for use in the featuredmethodologies.

The Fc binding agent is then washed with a buffered wash solutioncontaining a divalent cation salt to remove protein variant speciesbound to the solid phase or Fc binding agent. In particular, it has beendiscovered that the use of a divalent cation salt wash step can remove asignificant amount of undesirable impurities. Specifically, it has beendiscovered that intron read-through variants, low molecular weightvariants and under-disulfide bonded variants of a target protein can beremoved using a divalent cation salt wash. Moreover, host cell proteins(HCP) and DNA also can be removed using the divalent cation salt wash.In various embodiments, the divalent cation salt in the wash solutioncontains a chaotropic salt. Examples of suitable chaotropic saltsinclude, but are not limited to, calcium chloride (CaCl₂), nickelchloride (NiCl₂) and magnesium chloride (MgCl₂). While a single divalentcation salt can be present in the wash solution, in various embodiments,two or more divalent cation salts can be used.

In various embodiments, wash solutions in addition to the divalentcation salt containing wash solution are used to remove impurities. Forexample, in various embodiments a 20 to 50 mM Tris, 0.75 to 2.0 M NaCl,pH 5.0-9.0 solution, and/or a 10 mM Tris, pH 7.5 solution are used towash the Fc binding agent prior to, after, or both prior to and after,washing Fc binding agent with the divalent cation salt containing washsolution.

In various embodiments, the divalent cation salt is preferably added ata concentration between about 0.5 M and about 2.5 M to a pH bufferedsolution having a pH in the range from about 5 to about 9, andpreferably a pH in the range from about 7 to about 8. Preferredconcentrations of the divalent cation salt include, but are not limitedto, 0.6 M, 2.0 M and 2.5 M. Suitable buffers for this purpose include,but are not limited to, Tris or acetate buffers in a concentration from20 to 50 mM.

Following the washing step(s), the target protein is recovered from theFc binding agent. This is normally achieved using a suitable elutionbuffer. The target protein can, for example, be eluted from the columnusing an elution buffer having a low pH, e.g. in the range from about 2to about 6.5, and preferably in the range from about 2.5 to about 3.5.

In various embodiments, the target protein thus recovered can beformulated in a pharmaceutically acceptable carrier and used for variousdiagnostic, therapeutic or other uses known for such molecules.

In various embodiments, the eluted target protein preparation can besubjected to additional purification steps after the Fc binding agentchromatography step. For example, exemplary further purification stepsinclude, but are not limited to: anion exchange chromatography, cationexchange chromatography, hydrophobic interaction chromatography (HIC),hydroxyapatite chromatography, dialysis, affinity chromatography(including immobilized metal affinity chromatography), size exclusionchromatography (SEC), ammonium sulphate precipitation, ethanolprecipitation, reverse phase HPLC (RP-HPLC), chromatofocusing,ultrafiltration, diafiltration, and gel filtration. In variousembodiments, the Fc binding agent chromatography step is followed by ananion exchange chromatography and a HIC step. In various embodiments,the chromatography steps are further followed by a virus filtrationstep, an ultrafiltration/diafiltration step, and a microbial contaminantfiltration step. In various embodiments, these additional purificationsteps may be conducted prior to the Fc binding agent chromatographystep. In various aspects, the methods herein involve purifying an Fcregion-containing protein from impurities by Protein A chromatography.

In various embodiments, methods for purification of an Fc regioncontaining protein (the target protein) begin with adsorbing the targetprotein to an Fc binding agent comprising Protein A immobilized on asolid phase, followed by washing the Fc binding agent with a buffersolution containing a divalent cation salt to remove one or moreimpurities, and subsequently recovering the protein from the Protein Ato produce a first eluent pool.

In various embodiments, the purification process continues withsubjecting the first eluent pool to anion exchange chromatography bycontacting an anion exchange resin with the first eluent pool such thatimpurities adsorb to the resin, while the target protein does not adsorbto the resin. Thus, the target protein can be recovered from theflow-through to produce a second eluent pool. In various embodiments,the anion exchange chromatography step further comprises washing theanion exchange resin with a buffered wash solution to recover at least aportion of the adsorbed target protein, which would then be combinedwith the second eluent pool. Alternatively, the first eluent pool may becontacted with the anion exchange resin in such a way that the antibodyadsorbs, allowing any impurities to flow-through, optionally followed bywashing and eluting the adsorbed antibody.

In various embodiments, the purification process continues withsubjecting the second eluent pool to HIC by adsorbing the target proteinto a hydrophobic interaction resin (e.g., a solid phase functionalizedwith hydrophobic ligands), washing the hydrophobic interaction resinwith a buffered wash solution with an ionic strength which does notsubstantially elute the target protein, and recovering the targetprotein (typically using an elution buffer with an ionic strength lowenough to desorb the target protein from the hydrophobic interactionresin) on a third eluent pool. Alternatively, the second eluent pool maybe contacted with the HIC column in such a way that the target proteindoes not adsorb, recovering the flow-through target protein as a thirdeluent pool.

In various embodiments, the purification process includes one or morefiltration steps, for example, to remove viruses, concentrate and bufferthe solution containing the target protein, and to remove microbialcontaminants.

In various embodiments, the present invention provides methods for thepurification of a protein having an Fc region from a source liquidcomprising the protein and one or more impurities where the impuritiescomprise one or more IRT variants. In one embodiment, the methodsprovide for about a 2 to about a 20 fold reduction in IRT variant levelsfrom those in the source liquid. Preferably, IRT variant levels arereduced by at least 5 fold, and more preferably IRT variant levels arereduced by at least 10 fold. For example, in a source liquid (startingsample) having about 3-5% IRT antibody variants (as a percentage oftotal species in the source liquid) IRT antibody variant species can bereduced to about 0.3 to about 0.5%. In various embodiments, IRT variantspecies are reduced to: less than 1%, less than 0.8%, less than 0.5%,less than 0.3%, less than 0.2%, and/or less than 0.1%. Preferably, inthe purification of a source liquid for the preparation of a protein,IRT variants are reduced to: less than 1%, less than 0.8%, less than0.5%, less than 0.3%, less than 0.2%, and/or less than 0.1% as apercentage of total species in the source liquid.

In various embodiments, the present invention provides methods for thepurification of a protein having an Fc region from a source liquidcomprising the protein and one or more impurities where the impuritiescomprise one or more LMW variants. In one embodiment, the methodsprovide for about a 2 to about a 20 fold reduction in LMW variant levelsfrom those in the source liquid. Preferably, LMW variant levels arereduced by at least 5 fold, and more preferably LMW variant levels arereduced by at least 10 fold.

For example, in a source liquid (starting sample) having about 20% UDBantibody variants (as a percentage of total species in the sourceliquid) UDB antibody variant species can be reduced to about 10% toabout 2%. In various embodiments, UDB variant species are reduced to:less than 20%, less than 45%, less than 10%, less than 5%, less than 2%,or less than 1%. Preferably, in the purification of a source liquid forthe preparation of a protein, UDB variants are reduced to: less than20%, less than 15%, less than 10%, less than 5%, less than 2%, or lessthan 1% as a percentage of total species in the source liquid.

For example, in a source liquid (starting sample) having about 3-5% LMWantibody variants (as a percentage of total species in the sourceliquid) LMW antibody variant species can be reduced to about 0.3 toabout 0.5%. In various embodiments, LMW variant species are reduced to:less than 1%, less than 0.8%, less than 0.5%, less than 0.3%, less than0.2%, and/or less than 0.1%. Preferably, in the purification of a sourceliquid for the preparation of a protein, LMW variants are reduced to:less than 1%, less than 0.8%, less than 0.5%, less than 0.3%, less than0.2%, and/or less than 0.1% as a percentage of total species in thesource liquid.

In various embodiments, the present invention provides methods for thepurification of a protein having an Fc region from a source liquidcomprising the protein and one or more impurities where the impuritiescomprise one or more UDB variants. In one embodiment, the methodsprovide for about a 2 to about a 20 fold reduction in UDB variant levelsfrom those in the source liquid. Preferably, UDB variant levels arereduced by at least 5 fold, and more preferably UDB variant levels arereduced by at least 10 fold.

For example, in a source liquid (starting sample) having about 20% UDBantibody variants (as a percentage of total species in the sourceliquid) UDB antibody variant species can be reduced to about 10% toabout 2%. In various embodiments, UDB variant species are reduced to:less than 20%, less than 15%, less than 10%, less than 5%, less than 2%,or less than 1%. Preferably, in the purification of a source liquid forthe preparation of a protein, UDB variants are reduced to: less than20%, less than 15%, less than 10%, less than 5%, less than 2%, or lessthan 1% as a percentage of total species in the source liquid.

Also, for example, in a source liquid (starting sample) having about3-5% UDB antibody variants (as a percentage of total species in thesource liquid) UDB antibody variant species can be reduced to about 0.3to about 0.5%. In various embodiments, UDB variant species are reducedto: less than 1%, less than 0.8%, less than 0.5%, less than 0.3%, lessthan 0.2%, and/or less than 0.1%. Preferably, in the purification of asource liquid for the preparation of a protein, UDB variants are reducedto: less than 1%, less than 0.8%, less than 0.5%, less than 0.3%, lessthan 0.2%, and/or less than 0.1% as a percentage of total species in thesource liquid.

Proteins for Use in the Purification Methods of the Invention

The protein having an Fc region to be purified according to theinvention as described herein is prepared using techniques which arewell established in the art and include, for example, synthetictechniques (such as recombinant techniques and peptide synthesis or acombination of these techniques), or may be isolated from an endogenoussource of the protein. In certain embodiments of the invention, theprotein having an Fc region is an antigen-binding polypeptide, morepreferably, an antibody. The antibody can be, for example, a polyclonalantibody preparation, a monoclonal antibody, a recombinant antibody, achimeric antibody, a humanized antibody or a human antibody. Techniquesfor the production of an antigen-binding polypeptide, and in particular,antibodies, are described below. Alternatively, the protein having an Fcregion can be a modified form of an antibody, such as a bispecificantibody, an antibody conjugate or an antibody fusion protein (e.g., anFc fusion protein). Techniques for the production of such modified formsof antibodies and antibody fusion proteins also are described below.

Polyclonal Antibodies

Polyclonal antibodies can be prepared by immunizing a suitable subjectwith an immunogen. The antibody titer in the immunized subject can bemonitored over time by standard techniques, such as with an enzymelinked immunosorbent assay (ELISA) using immobilized target antigen. Ifdesired, the antibody molecules directed against the target antigen canbe isolated from the mammal (for example, from the blood) and furtherpurified by well known techniques, such as protein A Sepharosechromatography to obtain the antibody, for example, IgG, fraction. At anappropriate time after immunization, for example, when the anti-antigenantibody titers are highest, antibody-producing cells can be obtainedfrom the subject and used to prepare monoclonal antibodies by standardtechniques, such as the hybridoma technique originally described byKohler and Milstein (1975) Nature 256:495-497) (see also, Brown et al.(1981) J. Immunol. 127:539-46; Brown et al. (1980) J. Biol. Chem255:4980-83; Yeh et al. (1976) Proc. Natl. Acad. Sci. USA 76:2927-31;and Yeh et al. (1982) Int. J. Cancer 29:269-75). For the preparation ofchimeric polyclonal antibodies, see Buechler et al. U.S. Pat. No.6,420,113.

Monoclonal Antibodies

Any of the many well known protocols used for fusing lymphocytes andimmortalized cell lines can be applied for the purpose of generating amonoclonal antibody (see, for example, G. Galfre et al. (1977) Nature266:55052; Gefter et al. Somatic Cell Genet., cited supra; Lerner, YaleJ. Biol. Med., cited supra; Kenneth, Monoclonal Antibodies, citedsupra). Moreover, the ordinarily skilled worker will appreciate thatthere are many variations of such methods which also would be useful.

Typically, the immortal cell line (for example, a myeloma cell line) isderived from the same mammalian species as the lymphocytes. For example,murine hybridomas can be made by fusing lymphocytes from a mouseimmunized with an immunogenic preparation of the present invention withan immortalized mouse cell line. Preferred immortal cell lines are mousemyeloma cell lines that are sensitive to culture medium containinghypoxanthine, aminopterin and thymidine (“HAT medium”). Any of a numberof myeloma cell lines can be used as a fusion partner according tostandard techniques, for example, the P3-NS1/1-Ag4-1, P3-x63-Ag8.653 orSp2/O—Ag14 myeloma lines. These myeloma lines are available from ATCC.Typically, HAT-sensitive mouse myeloma cells are fused to mousesplenocytes using polyethylene glycol (“PEG”). Hybridoma cells resultingfrom the fusion are then selected using HAT medium, which kills unfusedand unproductively fused myeloma cells (unfused splenocytes die afterseveral days because they are not transformed). Hybridoma cellsproducing a monoclonal antibody of the invention are detected byscreening the hybridoma culture supernatants for antibodies that bind atarget antigen using a standard ELISA assay.

Recombinant Antibodies

Alternative to preparing monoclonal antibody-secreting hybridomas, amonoclonal antibody can be identified and isolated by screening arecombinant combinatorial immunoglobulin library (for example, anantibody phage display library) with a target antigen to thereby isolateimmunoglobulin library members that bind the target antigen. Kits forgenerating and screening phage display libraries are commerciallyavailable (for example, the Pharmacia Recombinant Phage Antibody System,Catalog No. 27-9400-01; and the Stratagene SurfZAP™ Phage Display Kit,Catalog No. 240612). Additionally, examples of methods and reagentsparticularly amenable for use in generating and screening antibodydisplay library can be found in, for example, Ladner et al. U.S. Pat.No. 5,223,409; Kang et al. PCT International Publication No. WO92/18619; Dower et al. PCT International Publication No. WO 91/17271;Winter et al. PCT International Publication WO 92/20791; Markland et al.PCT International Publication No. WO 92/15679; Breitling et al. PCTInternational Publication WO 93/01288; McCafferty et al. PCTInternational Publication No. WO 92/01047; Garrard et al. PCTInternational Publication No. WO 92/09690; Ladner et al. PCTInternational Publication No. WO 90/02809; Fuchs et al. (1991)Bio/Technology 9:1370-1372; Hay et al. (1992) Hum. Antibod. Hybridomas3:81-85; Huse et al. (1989) Science 246:1275-1281; Griffiths et al.(1993) EMBO J 12:725-734; Hawkins et al. (1992) J. Mol. Biol.226:889-896; Clarkson et al. (1991) Nature 352:624-628; Gram et al.(1992) Proc. Natl. Acad. Sci. USA 89:3576-3580; Garrad et al. (1991)Bio/Technology 9:1373-1377; Hoogenboom et al. (1991) Nuc. Acid Res.19:4133-4137; Barbas et al. (1991) Proc. Natl. Acad. Sci. USA88:7978-7982; and McCafferty et al. Nature (1990) 348:552-554.

Chimeric and Humanized Antibodies

Additionally, recombinant antibodies, such as chimeric and humanizedmonoclonal antibodies, comprising both human and non-human portions,which can be made using standard recombinant DNA techniques, are withinthe scope of the invention.

The term “humanized immunoglobulin” or “humanized antibody” refers to animmunoglobulin or antibody that includes at least one humanizedimmunoglobulin or antibody chain (i.e., at least one humanized light orheavy chain). The term “humanized immunoglobulin chain” or “humanizedantibody chain” (i.e., a “humanized immunoglobulin light chain” or“humanized immunoglobulin heavy chain”) refers to an immunoglobulin orantibody chain (i.e., a light or heavy chain, respectively) having avariable region that includes a variable framework region substantiallyfrom a human immunoglobulin or antibody and complementarity determiningregions (CDRs) (for example, at least one CDR, preferably two CDRs, morepreferably three CDRs) substantially from a non-human immunoglobulin orantibody, and further includes constant regions (for example, at leastone constant region or portion thereof, in the case of a light chain,and three constant regions in the case of a heavy chain). The term“humanized variable region” (for example, “humanized light chainvariable region” or “humanized heavy chain variable region”) refers to avariable region that includes a variable framework region substantiallyfrom a human immunoglobulin or antibody and complementarity determiningregions (CDRs) substantially from a non-human immunoglobulin orantibody.

The phrase “substantially from a human immunoglobulin or antibody” or“substantially human” means that, when aligned to a human immunoglobulinor antibody amino sequence for comparison purposes, the region shares atleast 80-90%, 90-95%, or 95-99% identity (i.e., local sequence identity)with the human framework or constant region sequence, allowing, forexample, for conservative substitutions, consensus sequencesubstitutions, germline substitutions, backmutations, and the like. Theintroduction of conservative substitutions, consensus sequencesubstitutions, germline substitutions, backmutations, and the like, isoften referred to as “optimization” of a humanized antibody or chain.The phrase “substantially from a non-human immunoglobulin or antibody”or “substantially non-human” means having an immunoglobulin or antibodysequence at least 80-95%, preferably at least 90-95%, more preferably,96%, 97%, 98%, or 99% identical to that of a non-human organism, forexample, a non-human mammal.

Accordingly, all regions or residues of a humanized immunoglobulin orantibody, or of a humanized immunoglobulin or antibody chain, except theCDRs, are substantially identical to the corresponding regions orresidues of one or more native human immunoglobulin sequences. The term“corresponding region” or “corresponding residue” refers to a region orresidue on a second amino acid or nucleotide sequence which occupies thesame (i.e., equivalent) position as a region or residue on a first aminoacid or nucleotide sequence, when the first and second sequences areoptimally aligned for comparison purposes.

The term “significant identity” means that two polypeptide sequences,when optimally aligned, such as by the programs GAP or BESTFIT usingdefault gap weights, share at least 50-60% sequence identity, preferablyat least 60-70% sequence identity, more preferably at least 70-80%sequence identity, more preferably at least 80-90% sequence identity,even more preferably at least 90-95% sequence identity, and even morepreferably at least 95% sequence identity or more (for example, 99%sequence identity or more). The term “substantial identity” means thattwo polypeptide sequences, when optimally aligned, such as by theprograms GAP or BESTFIT using default gap weights, share at least 80-90%sequence identity, preferably at least 90-95% sequence identity, andmore preferably at least 95% sequence identity or more (for example, 99%sequence identity or more). For sequence comparison, typically onesequence acts as a reference sequence, to which test sequences arecompared. When using a sequence comparison algorithm, test and referencesequences are input into a computer, subsequence coordinates aredesignated, if necessary, and sequence algorithm program parameters aredesignated. The sequence comparison algorithm then calculates thepercent sequence identity for the test sequence(s) relative to thereference sequence, based on the designated program parameters.

Optimal alignment of sequences for comparison can be conducted, forexample, by the local homology algorithm of Smith & Waterman, Adv. Appl.Math. 2:482 (1981), by the homology alignment algorithm of Needleman &Wunsch, J. Mol. Biol. 48:443 (1970), by the search for similarity methodof Pearson & Lipman, Proc. Nat'l. Acad. Sci. USA 85:2444 (1988), bycomputerized implementations of these algorithms (GAP, BESTFIT, FASTA,and TFASTA in the Wisconsin Genetics Software Package, Genetics ComputerGroup, 575 Science Dr., Madison, Wis.), or by visual inspection (seegenerally Ausubel et al., Current Protocols in Molecular Biology). Oneexample of algorithm that is suitable for determining percent sequenceidentity and sequence similarity is the BLAST algorithm, which isdescribed in Altschul et al., J. Mol. Biol. 215:403 (1990). Software forperforming BLAST analyses is publicly available through the NationalCenter for Biotechnology Information (publicly accessible through theNational Institutes of Health NCBI internet server). Typically, defaultprogram parameters can be used to perform the sequence comparison,although customized parameters can also be used. For amino acidsequences, the BLASTP program uses as defaults a wordlength (W) of 3, anexpectation (E) of 10, and the BLOSUM62 scoring matrix (see Henikoff &Henikoff, Proc. Natl. Acad. Sci. USA 89:10915 (1989)).

Preferably, residue positions which are not identical differ byconservative amino acid substitutions. For purposes of classifying aminoacids substitutions as conservative or nonconservative, amino acids aregrouped as follows: Group I (hydrophobic sidechains): leu, met, ala,val, leu, ile; Group II (neutral hydrophilic side chains): cys, ser,thr; Group III (acidic side chains): asp, glu; Group IV (basic sidechains): asn, gln, his, lys, arg; Group V (residues influencing chainorientation): gly, pro; and Group VI (aromatic side chains): trp, tyr,phe. Conservative substitutions involve substitutions between aminoacids in the same class. Non-conservative substitutions constituteexchanging a member of one of these classes for a member of another.

Preferably, humanized immunoglobulins or antibodies bind antigen with anaffinity that is within a factor of three, four, or five of that of thecorresponding non-humanized antibody. For example, if the nonhumanizedantibody has a binding affinity of 10⁻⁹ M, humanized antibodies willhave a binding affinity of at least 3×10⁻⁸ M, 4×10⁻⁸ M, 5×10⁻⁸ M, or10⁻⁹ M. An immunoglobulin chain is said to “direct antigen binding” whenit confers upon an intact immunoglobulin or antibody (or antigen bindingfragment thereof) a specific binding property or binding affinity. Amutation (for example, a backmutation) is said to substantially affectthe ability of a heavy or light chain to direct antigen binding if itaffects (for example, decreases) the binding affinity of an intactimmunoglobulin or antibody (or antigen binding fragment thereof)comprising said chain by at least an order of magnitude compared to thatof the antibody (or antigen binding fragment thereof) comprising anequivalent chain lacking said mutation. A mutation “does notsubstantially affect (for example, decrease) the ability of a chain todirect antigen binding” if it affects (for example, decreases) thebinding affinity of an intact immunoglobulin or antibody (or antigenbinding fragment thereof) comprising said chain by only a factor of two,three, or four of that of the antibody (or antigen binding fragmentthereof) comprising an equivalent chain lacking said mutation.

The term “chimeric immunoglobulin” or antibody refers to animmunoglobulin or antibody whose variable regions derive from a firstspecies and whose constant regions derive from a second species.Chimeric immunoglobulins or antibodies can be constructed, for exampleby genetic engineering, from immunoglobulin gene segments belonging todifferent species. The terms “humanized immunoglobulin” or “humanizedantibody” are not intended to encompass chimeric immunoglobulins orantibodies, as defined infra. Although humanized immunoglobulins orantibodies are chimeric in their construction (i.e., comprise regionsfrom more than one species of protein), they include additional features(i.e., variable regions comprising donor CDR residues and acceptorframework residues) not found in chimeric immunoglobulins or antibodies,as defined herein.

Such chimeric and humanized monoclonal antibodies can be produced byrecombinant DNA techniques known in the art, for example using methodsdescribed in Robinson et al. International Application No.PCT/US86/02269; Akira, et al. European Patent Application 184,187;Taniguchi, M., European Patent Application 171,496; Morrison et al.European Patent Application 173,494; Neuberger et al. PCT InternationalPublication No. WO 86/01533; Cabilly et al. U.S. Pat. No. 4,816,567;Cabilly et al. European Patent Application 125,023; Better et al. (1988)Science 240:1041-1043; Liu et al. (1987) Proc. Natl. Acad. Sci. USA84:3439-3443; Liu et al. (1987) J. Immunol. 139:3521-3526; Sun et al.(1987) Proc. Natl. Acad. Sci. USA 84:214-218; Nishimura et al. (1987)Canc. Res. 47:999-1005; Wood et al. (1985) Nature 314:446-449; and Shawet al. (1988) J. Natl. Cancer Inst. 80:1553-1559); Morrison, S. L.(1985) Science 229:1202-1207; Oi et al. (1986) BioTechniques 4:214;Winter U.S. Pat. No. 5,225,539; Jones et al. (1986) Nature 321:552-525;Verhoeyan et al. (1988) Science 239:1534; and Beidler et al. (1988) J.Immunol. 141:4053-4060.

Human Antibodies from Transgenic Animals and Phage Display

Alternatively, it is now possible to produce transgenic animals (forexample, mice) that are capable, upon immunization, of producing a fullrepertoire of human antibodies in the absence of endogenousimmunoglobulin production. For example, it has been described that thehomozygous deletion of the antibody heavy-chain joining region (J_(H))gene in chimeric and germ-line mutant mice results in completeinhibition of endogenous antibody production. Transfer of the humangerm-line immunoglobulin gene array in such germ-line mutant miceresults in the production of human antibodies upon antigen challenge.See, for example, U.S. Pat. Nos. 6,150,584; 6,114,598; and 5,770,429.

Fully human antibodies can also be derived from phage-display libraries(Hoogenboom et al., J. Mol. Biol., 227:381 (1991); Marks et al., J. Mol.Biol., 222:581-597 (1991)). Chimeric polyclonal antibodies can also beobtained from phage display libraries (Buechler et al. U.S. Pat. No.6;420,113).

Bispecific Antibodies and Antibody Conjugates

Bispecific antibodies (BsAbs) are antibodies that have bindingspecificities for at least two different epitopes. Such antibodies canbe derived from full length antibodies or antibody fragments (forexample F(ab)′2 bispecific antibodies). Methods for making bispecificantibodies are known in the art. Traditional production of full lengthbispecific antibodies is based on the coexpression of two immunoglobulinheavy chain-light chain pairs, where the two chains have differentspecificities (Millstein et al., Nature, 305:537-539 (1983)). Because ofthe random assortment of immunoglobulin heavy and light chains, thesehybridomas (quadromas) produce a potential mixture of different antibodymolecules (see, WO 93/08829 and in Traunecker et al., EMBO J.,10:3655-3659 (1991)).

Bispecific antibodies also include cross-linked or “heteroconjugate”antibodies. For example, one of the antibodies in the heteroconjugatecan be coupled to avidin, the other to biotin or other payload.Heteroconjugate antibodies may be made using any convenientcross-linking methods. Suitable cross-linking agents are well known inthe art, and are disclosed in U.S. Pat. No. 4,676,980, along with anumber of cross-linking techniques.

In yet another embodiment, the antibody can be conjugated, chemically orgenetically, to a payload such as a reactive, detectable, or functionalmoiety, for example, an immunotoxin to produce an antibody conjugate.Such payloads include, for example, immunotoxins, chemotherapeutics, andradioisotopes, all of which are well-known in the art.

Antibody Fusion Proteins

A protein having an Fc region as used in the invention can be a fusionprotein that contains at least the Fc portion of an antibody fused to anon-antibody protein or polypeptide. For example, the Fc region can befused to a ligand for a receptor such that a soluble fusion protein iscreated that is capable of binding the receptor and that has Fc-relatedfunctions (such as serum stability, Fc receptor binding and the like).Alternatively, the Fc region can be fused to the extracellular domain ofa receptor such that a soluble fusion protein is created that is capableof binding the ligand for the receptor (thereby competing with thenative receptor) and that has Fc-related functions. A non-limitingexample of such an Fc fusion protein is etanercept (Embrel®), whichcomprises the extracellular ligand-binding domain of the human TNFαreceptor fused to the Fc portion of human IgG1. Antibody fusion proteins(also referred to in the art as Fc fusion proteins or Ig fusionproteins) can be prepared using standard recombinant DNA techniques andhave been described in the art, see for example U.S. Pat. No. 5,116,964,U.S. Pat. No. 5,225,538, U.S. Pat. No. 5,336,603 and U.S. Pat. No.5,428,130, all by Capon et al.

Anti IL-13 Antibodies

In a preferred embodiment, the protein having an Fc region to bepurified according to the invention is an anti-IL-13 antibody.Anti-IL-13 antibodies are described in U.S. Provisional Application Ser.Nos. 60/578,473, filed Jun. 9, 2004 and 60/581,375, filed Jun. 22, 2004,both titled “Antibodies against human IL-13 and uses thereof.” Thecontents of these applications are incorporated by reference. Apreferred anti-IL-13 antibody may variously be referred to as “IMA”herein.

Antibodies that are capable of binding to, neutralizing and/orinhibiting one or more IL-13-associated activities, particularly thesignaling activity of IL-13, are useful for treating IL-13-mediateddiseases, such as allergic asthma, nonallergic asthma, andasthma-related pathologies, such as fibrosis, eosinophilia, and mucusproduction.

IL-13 binding agents that are IL-13 antagonists, including antibodiesand antigen-binding fragments thereof that bind to IL-13, in particular,human IL-13, with high affinity and specificity. The antibodies andantigen-binding fragments thereof of the present disclosure are alsoreferred to herein as “anti-IL-13 antibodies” and “fragments thereof,”respectively. In one embodiment, the anti-IL-13 antibody or fragmentthereof reduces, neutralizes, and/or antagonizes at least oneIL-13-associated activity. For example, the anti-IL-13 antibody orfragment thereof can bind to IL-13, e.g., an epitope of IL-13, andinterfere with an interaction, e.g., binding, between IL-13 and an IL-13receptor complex (“IL-13R”), e.g., a complex comprising IL-13 receptor(“IL-13Rα1”) and the interleukin-4 receptor alpha chain (“IL-4Rα”), or asubunit thereof (e.g., IL-13Rα1 or IL-4Rα, individually). Thus, theantibodies and fragments thereof described herein can be used tointerfere with (e.g., inhibit, block or otherwise reduce) aninteraction, e.g., binding, between IL-13 and an IL-13 receptor complex,or a subunit thereof, thereby interfering with the formation of afunctional signaling complex.

Other Preferred Fc Region Containing Proteins

In another preferred embodiment, the protein having an Fc region to bepurified according to the invention is an anti-Aβ antibody. Anti-Aβantibodies are described in PCT Publication No. WO 2002/46237 and U.S.Publication No. 20050118651, both titled “Humanized antibodies thatrecognize beta amyloid peptide.” The contents of these applications areincorporated by reference. Preferred anti-Aβ antibodies may variously bereferred to as “AAB” and “12A 11” herein.

Other preferred Fc region containing proteins include antibodies thathave been approved for therapeutic use in humans. Such antibodiesinclude antibodies that bind to a tumor cell antigen, antibodies thatbind to a cytokine, antibodies that bind to a cytokine receptor andantibodies that bind to an adhesion protein. Accordingly, in variousembodiments, an Fc region containing protein can be an antibody or an Fcfusion proteins that bind an antigen selected from the group consistingof CD3 (e.g., OKT3), CD52 (e.g., alemtuzumab; Campath®), VEGF (e.g.,bevacizumab; Avastin®), EGFR (e.g., cetuximab; Erbitux®), CD33 (e.g.,gemtuzumab; Mylotarg®), CD20 (e.g., rituximab; Rituxan®; tositumomab;Bexxar®; ibritumomab; Zevalin®), HER-2 (e.g., trastuzumab; Herceptin®),TNFα (e.g., adalimumab; Humira®, infliximab; Remicade®; etanercept;Embrel®), CD25 (e.g., daclizumab; Zenapax®; basiliximab; Simulect®), RSV(e.g., palivizumab; Synagis®), IgE (e.g., omalizumab; Xolair®), gpIIb/IIa (e.g., abciximab; Reopro®), CD11a (e.g., efalizumab; Raptiva®)and α4 integrin (e.g., natalizumab; Tysabri®).

It is understood that any of the foregoing polypeptide molecules, aloneor in combination, are suitable for preparation as Fc region containingproteins according to the invention.

Various aspects and embodiments of the present invention are furtherdescribed by way of the following Examples. The Examples are offered byway of illustration and not by way of limitation.

EXAMPLES

The following examples are offered for illustrative purposes only.

Examples are provided using three different monoclonal antibodies(referred to as AAB, 12A11 and IMA). Eight separate experiments aredescribed, each representing a combination of antibody and impurityremoval.

Materials and Methods

In general, the practice of the present invention employs, unlessotherwise indicated, conventional techniques of chemistry, molecularbiology, recombinant DNA technology, immunology (especially, e.g.,immunoglobulin technology), and standard techniques in electrophoresis.See, e.g., Sambrook, Fritsch and Maniatis, Molecular Cloning: ColdSpring Harbor Laboratory Press (1989); Antibody Engineering Protocols(Methods in Molecular Biology), 510, Paul, S., Humana Pr (1996);Antibody Engineering: A Practical Approach (Practical Approach Series,169), McCafferty, Ed., Irl Pr (1996); Antibodies: A Laboratory Manual,Harlow et al., C.S.H.L. Press, Pub. (1999); Current Protocols inMolecular Biology, eds. Ausubel et al., John Wiley & Sons (1992). Bousseet al., Protein Sizing on a Microchip, Anal. Chem. 73, 1207-1212 (2001);Knapp et al., Commercialized and Emerging Lab-on-a-Chip Applications;In: Proceedings of the μTAS 2001 Symposium, Ramsey, J. M. & van denBerg, A., 7-10 (2001); and Mhatre et al., Strategies for locatingdisulfide bonds in a monoclonal antibody via mass spectrometry, RapidCommun. Mass Spectrom, 13 (24) 2503-2510 (1999).

Production of Target Protein

The target Fc containing proteins can be produced by standard expressionmethods, e.g., using a recombinant mammalian cell line grown insuspension culture. Conditioned medium containing the Fc containingprotein of interest is generated in a production bioreactor. Theresulting product may be harvested and clarified with any appropriateclarification step such as, for example, either microfiltration and 0.22μm filtration or centrifugation, pad filtration and 0.22 μm filtration.

Purification of Target Protein

The purification of the target monoclonal antibodies exemplified herein(AAB, 12A11 and IMA) consists of capture of the target molecule onprotein A affinity chromatography. This can consist of rmp Protein ASepharose™ Fast Flow, Protein A Sepharose™ Fast Flow, or MabSelectProtein A. The resin is then washed as described for each of theexperiments and the product eluted and tested for impurity levels.

Analysis of Target Protein

Reversed-Phase HPLC (RP-HPLC) was used to quantitate the amount of IRTpresent in the AAB monoclonal antibody samples, while Pro A HPLC methodwas employed to determine IRT levels for the IMA monoclonal antibody.Size Exclusion Chromatography (SEC-HPLC) was used to determine thepercentage of monomeric protein (monomeric IgG), high molecular weight(HMW), and low molecular weight (LMW) species. Denaturing SEC-HPLCanalysis was carried out to determine the relative amount ofUnder-Disulfide Bonded (UDB) species in samples. The levels of HCP inthe test samples were determined using an Enzyme-Linked immunosorbantassay (ELISA).

Analytical Assays: IRT & UDB

Reversed-Phase HPLC (AAB IRT Analysis)

The RP-HPLC was conducted as follows. Disulfide reduction of each samplewas performed by incubation at 40° C. for 60 min in the presence of 2.5mM DTT. Alkylation was performed by incubation at room temperature inthe presence of 5.5 mM iodoacetic acid. Following reduction andalkylation, all samples were quenched with 5 μl of 1 M DTT. The limit ofquantification for this assay is 0.5%. Approximately 40 μg of eachreduced, alkylated sample was injected onto a POROS R1/H RP-HPLC columnand run for 70 min under the following conditions:

Column: Poros R1/H RP-HPLC Column Temp: 50° C.;

Mobile Phase A: 0.1% TFA (w/v) in water;

Mobile Phase B: 0.1% TFA (w/v) in 95% acetonitrile;

Flow rate: 1.0 mL/min

Detection: 217 nm

Run Time: 70 minutes

Injection: Triplicate of 40 μg each

The gradient times were as listed in TABLE 1. TABLE 1 Gradient times forRP-HPLC method Gradient Time % A % B 0-1 95 5  2 70 30 54 60 4055.1-70   95 5Protein A HPLC (IMA IRT Analysis)

The Protein A-HPLC was conducted as follows. A total of 100 μg perinjection on POROS Pro A column at room temperature for 35 minutes wasperformed under the following conditions:

Column: Poros Pro A 4.6×50 mm

Column Temp: ambient

Mobile Phase A: 50 mM Ammonium formate, pH 6.0

Mobile Phase B: 10 mM Ammonium formate, 0.8% formic acid

Flow rate: 2.0 mL/min

Detection: 280 nm

Run Time: 35 minutes

Injection: Triplicate of 100 μg each

The gradient times were as listed in table 2. TABLE 2 Gradient times forPro A column Gradient Time % A % B 0-5 100 0 25-30 55 45 30.5-35   100 0dSEC-HPLC (AAB UDB Analysis)

Denaturing SEC-HPLC was conducted as follows. The pretreatment ofsamples for the denaturing SEC assay involves a reagent/sample mixtureat final concentrations of 200 μg/mL of protein, 3 M Guanidine HCl, and100 mM Tris, at a pH of 7.4. The samples were heated at 80° C. for 20minutes while mixing through inversion. For this assay, two controls areemployed to allow a bracketing of UDB levels. Internal references withlow and high levels of UDB were used as controls.

Chromatographic/Assay conditions were as follows:

Column: Tosoh BioSep G3000 SWxl

Column Temp: Ambient

Mobile Phase: 3 M Guanidine HCl, 25 mM NaPO₄, pH 6.8

Gradient: Isocratic

Flow rate: 0.5 mL/min

Detection: 280 nm

Run Time: 50 minutes

Injection: Triplicate 50 μL (10 μg)

Example 1 Comparison of Wash Buffers for IRT removal (AAB)

In this example, an impure solution containing the monoclonal antibodyAAB was purified by adsorption onto a Protein A column followed by afirst wash with a wash buffer containing either CaCl₂, MgCl₂, NaCl orpropylene glycol.

The culture containing the monoclonal antibody was purified at smallscale using an rmp Protein A Sepharose™ FF column (8.9 mL) connected toa GE Healthcare ÄKTA FPLC chromatography system. For all the rmp ProteinA Sepharose™ FF chromatography steps described in experiment 1, thefollowing conditions were used. (Exceptions are noted in the individualexperimental descriptions).

Column dimensions —1.0 cm×11.4 cm

Operational flow rate —150 cm/hr

Equilibration 1-20 mM Tris, 150 mM NaCl, pH 7.5 (5 column volumes)

Flush —20 mM Tris, 150 mM NaCl, pH 7.5 (1 column volume)

Wash 1—Variable (See Table 3) except for run #1, which had no wash 1

Wash 2—20 mM Tris, 1.0 M NaCl, pH 7.5 (5 column volumes)

Wash 3—10 mM Tris, 75 mM NaCl, pH 7.5 (7 column volumes)

Elution —50 mM Glycine, 75 mM NaCl, pH 3.1 (6 column volumes)

Strip 1—20 mM Sodium Citrate, pH 2.7 (5 column volumes)

Strip 2—6 M Guanidine HCl (2 column volumes)

Strip wash —20 mM Tris, 150 mM NaCl, pH 7.5 (5 column volumes)

Storage —16% Ethanol (5 column volumes)

Run temperature: 2-8° C.

The rmp Protein A Sepahrose™ FF column runs were equilibrated with 5column volumes of 20 mM Tris, 150 mM NaCl, pH 7.5. The column was loadedat approximately 10 mg product/mL resin. Loading was followed by a 1column volume flush with equilibration buffer and 5 column volumes ofwash 1 solution. All Wash 1 solutions tested are outlined in Table 3.Wash 1 was included in all runs except for run #1. Wash 1 was followedby 5 column volumes of 20 mM Tris, 1.0 M NaCl, pH 7.5 and 7 columnvolumes of 10 mM Tris, 75 mM NaCl, pH 7.5. The monoclonal antibody waseluted from the column with 50 mM Glycine, 75 mM NaCl, pH 3.1. Theproduct pool was then neutralized to 7.9-8.1 with 2 M Tris pH 8.5. Thecolumns were then stripped, washed and stored. Table 3 lists the levelsof the IRT species & LMW present in the product pools from the variousruns. TABLE 3 IRT and LMW Values for Various Wash 1 Buffers Run % % #Condition LMW IRT 1 Control (No Wash 1) 4.4 2.5 2 20% Propylene Glycol,pH 7.5 4.7 2.5 3 50 mM Tris, 2.0 M Magnesium Chloride, pH 7.5 1.6 1.5 450 mM Tris, 2.5 M Magnesium Chloride, pH 7.5 1.5 1.3 5 50 mM Acetate,2.0 M Magnesium Chloride, 0.9 0.8 pH 4.5 6 50 mM Tris, 4.0 M SodiumChloride, pH 7.5 4.4 2.5 7 50 mM Tris, 2.0 M Calcium Chloride, pH 7.51.8 1.4 8 50 mM Tris, 2.5 M Calcium Chloride, pH 7.5 0.8 0.8

The results showed that the magnesium chloride and calcium chloridewashes reduced levels of IRT and LMW species, whereas the sodiumchloride and propylene glycol washes did not reduce IRT or LMW species.

Example 2 Protein A Chromatography with CaCl₂ Wash for IRT Removal

In this example, a larger scale antibody purification was carried outusing protein A chromatography with a CaCl₂ wash to remove IRT species.

The culture containing the monoclonal antibody was purified at pilotscale using a MabSelect Protein A column (2.4 L) connected to aMillipore K-Prime 400 chromatography system. The two MabSelect runs wereperformed as described below.

Column dimensions —13 cm×18 cm

Operational flow rate —150 cm/hr, 300 cm/hr

Equilibration 1—20 mM Tris, 150 mM NaCl, pH 7.5 (5 column volumes)

Flush —20 mM Tris, 150 mM NaCl, pH 7.5 (2 column volumes)

Wash 1—50 mM Tris, 2 M CaCl₂, pH 7.5 for run #1 and no wash 1 for run #2

Wash 2—20 mM Tris, 1.0 M NaCl, pH 7.5 (5 column volumes)

Wash 3—10 mM Tris, 75 mM NaCl, pH 7.5 (5 column volumes)

Elution —50 mM Glycine, 25 mM NaCl, pH 3.1 (6 column volumes)

Strip 1—50 mM Glycine, 0.5 M NaCl, pH 2.7 (5 column volumes)

Strip 2—6 M Guanidine HCl (2 column volumes)

Strip wash —20 mM Tris, 150 mM NaCl, pH 7.5 (5 column volumes)

Storage —16% Ethanol (5 column volumes)

Run temperature: 2-8° C.

The MabSelect Protein A column was equilibrated with 5 column volumes of20 mM Tris, 150 mM NaCl, pH 7.5. The columns were then loaded atapproximately 10 mg product/mL resin. This was followed by a 2 columnvolume flush with equilibration buffer and 5 column volumes of wash 1solution. This wash 1 solution consisted of 50 mM Tris, 2.0 M CaCl₂, pH7.5 for run 1, while it was left out entirely for run 2. Wash 1 was thenfollowed by 5 column volumes of 50 mM Tris, 1.0 M NaCl, pH 7.5 and 5column volumes of 10 mM Tris, 75 mM NaCl, pH 7.5. The monoclonalantibody was eluted from the MabSelect Protein A column with 50 mMGlycine, 25 mM NaCl, pH 3.1. The product pool was then neutralized to7.8-8.2 with 2 M Tris pH 8.5. The columns were then stripped, washed andstored. The results are shown in Table 4. TABLE 4 % IRT levels inpilot-scale runs with and without calcium chloride wash Run # Wash 1Buffer % IRT 1 50 mM Tris, 2 M CaCl₂, pH 7.5 0.8 2 Control (None) 1.9

The results showed that at pilot scale the calcium chloride wash removedIRT from the product pool.

Example 3 IRT Removal (IMA)

In this example, a different monoclonal antibody (IMA) from that used inExample 1 was used in a small scale purification with a CaCl₂ wash.

The culture containing the different monoclonal antibody (IMA) waspurified at small scale using a MabSelect Protein A column (17.3 mL)connected to a GE Healthcare ÄKTA Explorer chromatography system. Therun was performed as described below.

Column dimensions —1.1 cm×18.2 cm (17.3 mL)

Operational flow rate —300 cm/hr

Equilibration 1—20 mM Tris, 150 mM NaCl, pH 7.5 (5.1 column volumes)

Wash 1—20 mM Tris, 1 M NaCl, pH 7.5 (5 column volumes)

Wash 2—50 mM Sodium Acetate, 0.6 M CaCl₂, pH 5.0 (5 column volumes)

Wash 3—0.50 mM Tris, 5 mM NaCl, pH 7.5 (3 column volumes)

Wash-4—10 mM Tris, 5 mM NaCl, pH 7.5 (5 column volumes)

Elution —50 mM Glycine, 5 mM NaCl, pH 3.0 (5 column volumes)

Strip —6 M Guanidine HCl (5 column volumes)

Strip wash —20 mM Tris, 150 mM NaCl, pH 7.5 (6 column volumes)

Storage —16% Ethanol (5 column volumes)

Run temperature: 18-24° C.

MabSelect protein A column was equilibrated with 5 column volumes of 20mM Tris, 1 M NaCl, pH 7.5. The column was loaded at approximately 45 mgproduct/mL resin. The column was then washed as follows: 5 columnvolumes of 20 mM Tris, 1.0 M NaCl, pH 7.5, 5 column volumes of 50 mMSodium Acetate, 0.6 M CaCl₂, pH 5.0, 3 column volumes of 50 mM Tris, 5mM NaCl, pH 7.5, and 5 column volumes of 10 mM Tris, 5 mM NaCl, pH 7.5.The product was eluted from the MabSelect protein A column with 50 mMGlycine, 5 mM NaCl, pH 3.0. The product pool was then neutralized to 7.7with 2 M Tris pH 8.0. The column was then stripped, washed and stored.The results are shown in Table 5, which provides the levels of IRTspecies in the load and peak. TABLE 5 % IRT in the load and peak in runwith CaCl₂ wash % IRT in Load % IRT in Peak 5.8 1.1

The results showed that the 0.6 M CaCl₂ wash provided a 5-fold reductionof IRT.

Example 4 Host Cell Protein Removal (IMA)

In this example, the ability of a CaCl₂ wash to remove host cell protein(HCP) from a preparation containing the IMA monoclonal antibody wasexamined.

The culture containing the monoclonal antibody was purified at smallscale using a MabSelect Protein A column (19 mL) connected to a GEHealthcare ÄKTA FPLC chromatography system. The two MabSelect runs wereperformed as described below.

Column dimensions —1.1 cm×20.0 cm (19 mL)

Operational flow rate —300 cm/hr

Equilibration 1—20 mM Tris, 150 mM NaCl, pH 7.5 (5.0 column volumes)

Wash 1—20 mM Tris, 1 M NaCl, pH 7.5 (5 column volumes)

Wash 2—50 mM Sodium Acetate, 0.6 M CaCl₂, pH 5.0 (5 column volumes; onlyfor run 2)

Wash 3—50 mM Tris, 5 mM NaCl, pH 7.5 (2 column volumes)

Wash 4—10 mM Tris, 5 mM NaCl, pH 7.5 (5 column volumes)

Elution —50 mM Glycine, 5 mM NaCl, pH 3.0 (5 column volumes)

Strip —6 M Guanidine HCl (5 column volumes)

Strip wash —20 mM Tris, 150 mM NaCl, pH 7.5 (6 column volumes)

Storage —16% Ethanol (5 column volumes)

Run temperature: 18-24° C.

The MabSelect protein A column was equilibrated with 5 column volumes of20 mM Tris, 150 mM NaCl, pH 7.5. The column was loaded at approximately45 mg product/mL resin. The column was then washed with 5 column volumesof 20 mM Tris, 1.0 M NaCl, pH 7.5; for Run 2 an additional wash with 5column volumes of 50 mM Sodium Acetate, 0.6 M CaCl₂, pH 5.0 was used.Prior to elution, the column was then washed with 5 column volumes of 50mM Tris, 5 mM NaCl, pH 7.5 and 5 column volumes of 10 mM Tris, 5 mMNaCl, pH 7.5. The product was eluted from the MabSelect protein A columnwith 50 mM Glycine, 5 mM NaCl, pH 3.0. The product pool was thenneutralized to pH 7.7 with 2 M Tris pH 8.0. The column was thenstripped, washed and stored. The results are shown in Table 6, whichprovides the level of HCP species present in the control run and the runwashed with CaCl₂. TABLE 6 HCP removal with and without CaCl₂ wash Run #Wash 2 Condition HCP (PPM) 1 None (Control) 6,124 2 50 mM SodiumAcetate, 0.6 M CaCl₂, pH 5.0 2,295

The results showed that the CaCl₂ wash provided 3 fold greater removalof HCP as compared to the control run.

Example 5 DNA Removal (AAB)

In this example, the ability of a CaCl₂ wash to remove host cell DNAfrom a preparation containing the AAB monoclonal antibody was examined.

The culture containing the monoclonal antibody was purified at smallscale using a MabSelect Protein A column (19 mL) connected to a GEHealthcare ÄKTA FPLC chromatography system. The three MabSelect runswere performed as described below.

Column dimensions —1.1 cm×20 cm

Operational flow rate —300 cm/hr

Equilibration 1—20 mM Tris, 150 mM NaCl, pH 7.5 (5 column volumes)

Flush —20 mM Tris, 150 mM NaCl, pH 7.5 (2 column volumes)

Wash 1—50 mM Tris, 2.0 M CaCl₂, pH 7.5 (5 column volumes) (Runs 2 and 3only)

Wash 2—20 mM Tris, 1.0 M NaCl, pH 7.5 (5 column volumes) (Runs 1 and 3only)

Wash 3—10 mM Tris, 75 mM NaCl, pH 7.5 (7 column volumes)

Elution —50 mM Glycine, 75 mM NaCl, pH 3.0 (6 column volumes)

Strip —50 mM Glycine, 0.5 M NaCl, pH 2.7 (5 column volumes)

Strip wash —20 mM Tris, 150 mM NaCl, pH 7.5 (5 column volumes)

Storage —16% Ethanol (5 column volumes)

Run temperature: 18-24° C.

The MabSelect Protein A column runs were equilibrated with 5 columnvolumes of 20 mM Tris, 150 mM NaCl, pH 7.5. The columns were then loadedat a load of approximately 40 mg product/mL resin. This was followed bya 2 column volume flush with equilibration buffer. For runs 2 and 3,this step was followed by 5 column volumes of Wash 1 solution. For runs1 and 3, 5 column volumes of Wash 2 solution was used. All 3 runsemployed 7 column volumes of Wash 3 solution. The monoclonal antibodywas eluted off the MabSelect Protein A column with 50 mM Glycine, 75 mMNaCl, pH 3.0. The product pool was then neutralized to 7.5-8.0 with 2 MTris pH 8.5. The columns were then stripped, washed and stored. Theresults are shown in Table 7. TABLE 7 DNA removal with calcium chloridewash. Run DNA DNA # Wash 1 Wash 2 (ng/mL) (ppm) 1 None (Control) 20 mMTris, 1 M NaCl, 3.6 0.37 pH 7.5 2 50 mM Tris, None 0.9 0.09 2 M CaCl₂,pH 7.5 3 50 mM Tris, 20 mM Tris, 1 M NaCl, 0.3 0.03 2 M CaCl₂, pH 7.5 pH7.5

The results showed that the addition of 50 mM Tris, 2.0 M calciumchloride, pH 7.5 provided 10 fold greater reduction of DNA compared tousing NaCl in the wash solution.

Example 6 Host Cell Protein (HCP) Removal (12A11)

In this example, a third monoclonal antibody, 12A11, was used inpurification runs in which various wash conditions were tested for theability to remove HCP.

A high throughput screen (HTS) in a 96-well filter plate format wasperformed to identify the best wash conditions for removal of impuritiessuch as HCP for the MabSelect step. This screen varied the washexcipients, excipient concentration, and pH to determine their effect onprocess related impurities such as HCP.

The MabSelect resin was equilibrated using 5 mM Tris, 10 mM NaCl, pH 7.3and loaded with product in a column. The resin was then unpacked, mixedand 50 μL of resin was distributed to each well of a 96 well filterplate. The resin in each well was equilibrated in solution of 5 mM Tris,10 mM-NaCl, pH 7.3, and then washed with each of the various excipientwash solutions in 3 stages, each using 300 μL of wash buffer. After theexcipient wash, a second wash with 5 mM Tris, 10 mM NaCl, pH 7.3 bufferwas performed in 4 stages of 300 μL each. The product was then elutedfrom the resin in 3 stages of 300 μL each. Elution stages 1 and 2 werecombined and tested for HCP levels.

Resin Volume —50 μL

Wash Excipients—Sodium Chloride, Calcium Chloride, Magnesium Chloride,

Excipient Concentrations —100, 250, 500, 1000, 1500, and 2000 mM

Excipient pH —6.0 & 7.5

Elution Buffers —25 mM Hepes, 10 mM NaCl, pH 3.0, 25 mM Hepes, 100 mMNaCl,

-   -   pH 3.0, 50 mM Glycine, 10 mM NaCl, pH 3.0, 50 mM Glycine, 100    -   mM NaCl, pH 3.0 and 100 mM Arginine, 10 mM NaCl, pH 3.0, 100    -   mM Arginine, 100 mM NaCl, pH 3.0        Run temperature: 18-24° C.

The results are shown in Tables 8 and 9. TABLE 8 HCP values forMabSelect resin washed with sodium chloride, calcium chloride, ormagnesium chloride at pH 6.0 Elution Wash NaCl Excipient Wash ExcipientConc. Conc. NaCl CaCl₂ MgCl₂ Elution Buffer (mM) (mM) HCP (ppm) 50 mMGlycine 10 100 46,800 28,500 30,800 25 mM HEPES 250 35,300 17,900 22,000100 mM Arginine 500 40,900 17,700 18,400 50 mM Glycine 1000 34,30012,600 14,200 25 mM HEPES 1500 37,000 7,800 10,700 100 mM Arginine 200043,900 5,800 9,300

TABLE 9 HCP values for MabSelect resin washed with sodium chloride,calcium chloride, or magnesium chloride at pH 7.5. Elution Wash NaClExcipient Wash Excipient Conc. Conc. NaCl CaCl₂ MgCl₂ Elution Buffer(mM) (mM) HCP (ppm) 50 mM Glycine 100 100 27,900 17,900 21,800 25 mMHEPES 250 24,700 16,600 18,200 100 mM Arginine 500 26,500 14,000 17,30050 mM Glycine 1000 30,100 14,500 17,700 25 mM HEPES 1500 35,300 12,00012,500 100 mM Arginine 2000 41,700 8,200 11,700

The results showed that both calcium chloride and magnesium chloridereduced the level of HCP in the MabSelect peak pool compared to sodiumchloride at pH 6.0 (Table 8) and pH 7.5 (Table 9) at all excipientconcentrations.

Example 7 Removal of Under-Disulfide Bonded Species (UDB)

In this example, the ability of the CaCl₂ wash to remove under disulfidebonded species (UDB) was examined.

Two rmp Protein A Sepharose™ FF runs were performed essentially asdescribed in example 1.

Column dimensions —1.0 cm×11.4 cm

Operational flow rate —150 cm/hr

Equilibration 1—20 mM Tris, 150 mM NaCl, pH 7.5 (5 column volumes)

Flush —20 mM Tris, 150 mM NaCl, pH 7.5 (1 column volume)

Wash 1—50 mM Acetate, 2.0 M CaCl₂, pH 5.0 for Run 1; None for Run 2

Wash 2—20 mM Tris, 1.0 M NaCl, pH 7.5 (5 column volumes)

Wash 3—10 mM Tris, 75 mM NaCl, pH 7.5 (7 column volumes)

Elution —50 mM Glycine, 75 mM NaCl, pH 3.1 (6 column volumes)

Strip 1—20 mM Sodium Citrate, pH 2.7 (5 column volumes)

Strip 2—6 M Guanidine HCl (2 column volumes)

Strip wash —20 mM Tris, 150 mM NaCl, pH 7.5 (5 column volumes)

Storage —16% Ethanol (5 column volumes)

Run temperature: 2-8° C.

The rmp Protein A Sepharose FF columns were equilibrated with 5 columnvolumes of 20 mM Tris, 150 mM NaCl, pH 7.5. The columns were then loadedat a load of approximately 10 mg product/mL resin. This was followed bya 1 column volume flush with equilibration buffer and then 5 columnvolumes of wash 1 solution. This wash 1 solution consisted of 50 mMAcetate, 2.0 M CaCl₂, pH 5.0 for run 1, while it was left out entirelyfor run 2. Wash 1 was then followed by 5 column volumes of 20 mM Tris,1.0 M NaCl, pH 7.5 and 7 column volumes of 10 mM Tris, 75 mM NaCl, pH7.5. The monoclonal antibody was eluted off the rmp Protein A Sepharose™FF column with 50 mM Glycine, 75 mM NaCl, pH 3.1. The product pool wasthen neutralized to 7.8-8.2 with 2 M Tris pH 8.5. The columns were thenstripped, washed and stored. The results are shown in Table 10. TABLE 10% UDB for with and without calcium washed samples. Run # Sample % UDB 150 mM Acetate, 2.0 M CaCl₂, pH 5.0 9.5 2 None (Control) 20.8

A 2-fold reduction in UDB levels was observed for the run that had theadditional 50 mM Acetate, 2.0 M CaCl₂, pH 5.0 wash.

Example 8 Removal of HCP and IRT with Other Divalent Cation Salt Washes(AAB)

In this example, the ability of washes containing either MnCl₂ or NiCl₂to remove impurities from a preparation containing the AAB monoclonalantibody was examined.

Two runs were performed to evaluate the effect of washes containingother divalent cationic salts such as MnCl₂ and NiCl₂. Two control runswere also performed—one using a 50 mM Tris, 1.0 M NaCl, pH 7.5 wash (noIRT or HCP removal expected) and another using a 50 mM Tris, 2.0 MCaCl₂, pH 7.5 wash.

The culture containing the monoclonal antibody was purified at smallscale using a MabSelect Protein A column (9 mL) connected to a GEHealthcare ÄKTA FPLC chromatography system. The MabSelect runs wereperformed as described below. As described below, all operationalparameters were identical for the four runs except for Wash 1, which wasvariable (Table 11).

Column dimensions —1.0 cm×11.5 cm (9 mL)

Operational flow rate —300 cm/hr (Equilibration, Wash 2, Elution,Regeneration,

Storage)

Operational flow rate —230 cm/hr (Load, Flush, Wash 1)

Equilibration 1—50 mM Tris, 150 mM NaCl, pH 7.5 (5.0 column volumes)

Wash 1—Variable (See Table 11 for composition)

Wash 2—50 mM Tris, 10 mM NaCl, pH 7.5 (5 column volumes)

Elution —50 mM Glycine, 10 mM NaCl, pH 3.0 (3 column volumes)

Regeneration —50 mM NaOH, 0.5 M Na₂SO₄ (5 column volumes)

Storage —16% Ethanol, 50 mM Tris, 150 mM NaCl, pH 7.5 (5 column volumes)

Run temperature: 18-24° C.

The MabSelect Protein A column was equilibrated with 5 column volumes of50 mM Tris, 150 mM NaCl, pH 7.5. The column was loaded at approximately40 mg product/mL resin. The remaining load was flushed out of the columnwith 5 column volumes of 50 mM Tris, 150 mM NaCl, pH 7.5. The column wasthen washed with one of the solutions described in Table 11. Prior toelution the column was washed with 5 column volumes of 50 mM Tris, 10 mMNaCl, pH 7.5. The product was eluted from the MabSelect Protein A columnwith 50 mM Glycine, 10 mM NaCl, pH 3.0. The product pool was thenneutralized to pH 8.0 with 2 M Tris pH 9.0. The column was stripped with5 column volumes 50 mM NaOH, 0.5 M Na₂SO₄ then stored with 5 columnvolumes of 16% ethanol, 50 mM Tris, 150 mM NaCl, pH 7.5. The results areshown in Table 11 (HCP removal) and Table 12 (IRT removal). TABLE 11 HCPremoval with various wash solutions Run # Wash 1 Condition HCP (PPM) 150 mM Tris, 1.0 M NaCl, pH 7.5 17,600 2 50 mM Sodium Acetate, 1.5 MMnCl₂, pH 5.0* 10,600 3 50 mM Sodium Acetate, 1.5 M NiCl₂, pH 5.0* 4,7004 50 mM Tris, 2.0 M CaCl₂, pH 7.5 6,500*pH 5.0 was chosen due to solubility of MnCl₂ and NiCl₂

TABLE 12 IRT Removal with various wash solutions Run # Wash 1 ConditionIRT (%) 1 50 mM Tris, 1.0 M NaCl, pH 7.5 2.78 2 50 mM Sodium Acetate,1.5 M MnCl₂, pH 5.0* 0.77 3 50 mM Sodium Acetate, 1.5 M NiCl₂, pH 5.0*0.47 4 50 mM Tris, 2.0 M CaCl₂, pH 7.5 0.87pH 5.0 was chosen due to solubility of MnCl₂ and NiCl₂

Table 11 shows that the level of HCPs present in runs that were washedwith solutions containing divalent cations had 1.5-3.5 fold less HCPsthan the control (1.0 M NaCl Wash). Table 12 shows that the runs thatcontained the washes with divalent cationic salts solutions alsoprovide>3.5 fold IRT removal compared to the run with a 1.0 M NaClcontaining wash solutions. Thus, these results demonstrated that saltwashes with other divalent cations (e.g., with MnCl₂ or NiCl₂),different than CaCl₂, also were effective in removing impurities.

Equivalents Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific embodiments of the invention described herein. Suchequivalents are intended to be encompassed by the following claims.

1. A method for purifying a protein having an Fc region from a sourceliquid comprising the protein and one or more impurities, comprising thesteps of: adsorbing the protein to an Fc binding agent; washing the Fcbinding agent with a buffer solution containing a divalent cation saltto remove one or more impurities; and recovering the protein from the Fcbinding agent in an elution solution.
 2. The method of claim 1, whereinsaid one or more impurities are selected from the group consisting of:intron read through variant species (IRT), under disulfide bondedspecies (UDB), and low molecular weight species (LMW).
 3. The method ofclaim 2, wherein said one or more impurities is an IRT.
 4. The method ofclaim 1, wherein the protein is an antibody.
 5. The method of claim 4,wherein the antibody is selected from the group consisting of: anantibody fusion, a murine antibody, a chimeric antibody, a humanizedantibody, and a human antibody.
 6. The method of claim 4, wherein theantibody is an anti-IL-13 antibody.
 7. The method of claim 4, whereinthe antibody binds to an antigen selected from the group consisting of:CD3, CD52, VEGF, EGFR, CD33, CD20, HER-2, TNFα, CD25, RSV, IgE, gpIIb/IIIa, CD11a and α4 integrin.
 8. The method of claim 1, wherein theprotein having an Fc region is recombinantly produced.
 9. The method ofclaim 1, wherein the protein having an Fc region is recombinantlyproduced in a Chinese Hamster Ovary (CHO) cell.
 10. The method of claim1, wherein the Fc binding agent comprises one or more of Protein A andProtein G.
 11. The method of claim 1, wherein the Fc binding agent isimmobilized on a solid phase.
 12. The method of claim 11, wherein thesolid phase comprises one or more of a bead, a gel, a resin, and aparticle.
 13. The method of claim 1, wherein the divalent cation saltcomprises a chaotropic salt.
 14. The method of claim 1, wherein thedivalent cation salt is selected from the group consisting of: CaCl₂,MgCl₂, NiCl₂ and mixtures thereof.
 15. The method of claim 1, whereinthe buffer solution containing the divalent cation salt has a pH valuein a range between about 4 to about
 8. 16. The method of claim 1,wherein the buffer solution containing the divalent cation salt has a pHvalue in a range between about 4.5 to about 7.5.
 17. The method of claim1, wherein the buffer solution has a divalent cation salt concentrationin a range between about 0.1 M to about 5 M.
 18. The method of claim 17,wherein the buffer solution has a divalent cation salt concentration ina range between about 0.5 M to about 3 M.
 19. The method of claim 1,wherein the buffer solution containing a divalent cation salt comprisesat least about 0.6 M CaCl₂.
 20. The method of claim 1, wherein thebuffer solution containing a divalent cation salt comprises at leastabout 2 M MgCl₂.
 21. The method of claim 1, wherein the buffer solutioncontaining a divalent cation salt comprises at least about 2 M CaCl₂.22. The method of claim 1, wherein the steps of adsorbing the protein toan Fc binding agent and washing the Fc binding agent are performed at atemperature in a range between about 2° C. to about 24° C.
 23. Themethod of claim 1, wherein the one or more impurities comprise one ormore of a host cell protein, a host cell DNA, a cell culture protein,and mixtures thereof.
 24. The method of claim 1, wherein the one or moreimpurities comprise an undesired species of the protein having an Fcregion.
 25. The method of claim 24, wherein the undesired species of theprotein having an Fc region comprises one or more of antibody chains orfragments thereof having intronic read through sequence, one or moreantibody chains or fragments thereof having an improper disulfidelinkage, a half-antibody or fragment thereof, a light chain dimer orfragment thereof, and a heavy chain dimer or fragment thereof.
 26. Themethod of claim 1, wherein the step of recovering the protein from theFc binding agent comprises eluting the protein using an elution bufferhaving a pH in a range from about 2.0 to about 6.5.
 27. The method ofclaim 1, wherein the method further comprises a chromatography stepselected from the group consisting of: anion exchange chromatography,cation exchange chromatography, immobilized metal affinitychromatography and hydrophobic interaction chromatography (HIC).
 28. Themethod of claim 1, wherein the method further comprises a chromatographystep selected from the group consisting of: hydroxyapatitechromatography, dialysis, affinity chromatography, ammonium sulphateprecipitation, ethanol precipitation, reverse phase HPLC (RP-HPLC), andchromatofocusing.
 29. The method of claim 1, wherein the one or moreimpurities comprise one or more intron read-through variants of theprotein and the elution solution containing the protein has a level ofintron read-through variants that is at least 5 fold less than the levelof intron read-through variants in the source liquid.
 30. The method ofclaim 29, wherein a solution containing the protein recovered in theelution solution has a level of intron read-through variants that is atleast 10 fold less than the level of intron read-through variants in thesource liquid.
 31. The method of claim 1, wherein the one or moreimpurities comprise one or more intron read-through variants of theprotein and the intron read-through variants comprise less than about 1%of a species of said protein in the elution solution.
 32. The method ofclaim 31, wherein the intron read-through variants comprise less thanabout 0.8% of a species of said protein in the elution solution.
 33. Themethod of claim 32, wherein the intron read-through variants compriseless than about 0.5% of a species of said protein in the elutionsolution.
 34. The method of claim 33, wherein the intron read-throughvariants comprise less than about 0.2% of a species of said protein inthe elution solution.
 35. The method of claim 1, wherein the one or moreimpurities comprise one or more low molecular weight species of theprotein and the low molecular weight species comprise less than about 1%of a species of said protein in the elution solution.
 36. The method ofclaim 35, wherein the low molecular weight species comprise less thanabout 0.8% of a species of said protein in the elution solution.
 37. Themethod of claim 36, wherein the low molecular weight species compriseless than about 0.5% of a species of said protein in the elutionsolution.
 38. The method of claim 37, wherein the low molecular weightspecies comprise less than about 0.2% of a species of said protein inthe elution solution.
 39. The method of claim 1, wherein the one or moreimpurities comprise one or more under-disulfide bonded variants of theprotein and the under-disulfide bonded variants comprise less than about15% of a species of said protein in the elution solution.
 40. The methodof claim 39, wherein the under-disulfide bonded variants comprise lessthan about 10% of a species of said protein in the elution solution. 41.The method of claim 40, wherein the under-disulfide bonded variantscomprise less than about 5% of a species of said protein in the elutionsolution.
 42. The method of claim 41, wherein the under-disulfide bondedvariants comprise less than about 2% of a species of said protein in theelution.
 43. A protein purified according to the method of claim
 1. 44.The protein of claim 43, wherein the protein is an antibody.
 45. A kitcomprising reagents for purifying a protein having an Fc region fromimpurities, the kit comprising, a reagent selected from the groupconsisting of: a divalent cation salt, and a Fc binding agent, andinstructions for use.